chore(studio): remove fully rolled-out studio feature flags (#2889)

## What

Removes six Studio feature flags that have been default-`true` for 7+ weeks. Each is reachable under two env names, so this deletes **12 `VITE_STUDIO_*` env vars**:

| Flag constant | Env names removed | Default-on since |
|---|---|---|
| `STUDIO_PREVIEW_MANUAL_EDITING_ENABLED` | `VITE_STUDIO_ENABLE_PREVIEW_MANUAL_DRAGGING`, `VITE_STUDIO_PREVIEW_MANUAL_EDITING_ENABLED` | 2026-05-12 |
| `STUDIO_INSPECTOR_PANELS_ENABLED` (+ its `STUDIO_PREVIEW_SELECTION_ENABLED` alias) | `VITE_STUDIO_ENABLE_INSPECTOR_PANELS`, `VITE_STUDIO_INSPECTOR_PANELS_ENABLED` | 2026-05-12 |
| `STUDIO_BLOCKS_PANEL_ENABLED` | `VITE_STUDIO_ENABLE_BLOCKS_PANEL`, `VITE_STUDIO_BLOCKS_PANEL_ENABLED` | 2026-05-18 |
| `STUDIO_GSAP_PANEL_ENABLED` | `VITE_STUDIO_ENABLE_GSAP_PANEL`, `VITE_STUDIO_GSAP_PANEL_ENABLED` | 2026-05-28 |
| `STUDIO_KEYFRAMES_ENABLED` | `VITE_STUDIO_ENABLE_KEYFRAMES`, `VITE_STUDIO_KEYFRAMES_ENABLED` | 2026-06-05 |
| `STUDIO_RAZOR_TOOL_ENABLED` | `VITE_STUDIO_ENABLE_RAZOR_TOOL`, `VITE_STUDIO_RAZOR_TOOL_ENABLED` | 2026-06-10 |

## Why

Every one of these shipped as a rollout gate, went to `true`, and then stayed. Because none of them was ever flipped back, the `false` branch was unreachable in practice while still costing a real import, a real conditional, and a real "what happens if this is off?" question at ~90 call sites across 25 files.

The bigger cost is what the dead branch kept alive. Removing the flags also removes the disabled-Studio code paths that only existed to serve them:

- the greyed-out, `disabled`, "Manual editing is temporarily disabled" Inspector button in `StudioHeader` (and the `STUDIO_MANUAL_EDITING_DISABLED_TITLE` constant behind it)
- the inspector-off reset `useEffect` in `useDomSelection`, which force-cleared selection and redirected the right panel to Renders
- three selection kill-switch early-returns in `useDomSelection` (`applyDomSelection`, `handleTimelineElementSelect`, `applyMarqueeSelection`)
- the tab-redirect branch in `normalizeStudioUrlPanelTab`, whose `options.inspectorPanelsEnabled` parameter had no production caller at all (only tests passed it)

## How

No behavior change: every flag was removed by keeping its default-`true` side.

The call-site edits are three mechanical boolean shapes (`X && rest` → `rest`, `rest && X` → `rest`, `!X || rest` → `rest`), applied by script for uniformity. Everything else (ternaries, `if` guards, unreachable blocks, JSX wrappers that had no other condition) was done by hand and the whole diff was read line by line afterwards.

`resolveStudioBooleanEnvFlag` and the `import.meta.env` / `window.__HF_STUDIO_ENV__` plumbing stay: three flags still use them (`STUDIO_FLAT_INSPECTOR_ENABLED`, `STUDIO_SDK_CUTOVER_ENABLED`, `STUDIO_SDK_RESOLVER_SHADOW_ENABLED`). Its unit tests kept their coverage but now exercise a live flag pair instead of retired env names, so no dead `VITE_STUDIO_*` string is left in the repo.

Net **-191 lines** (236 insertions, 427 deletions across 25 files); most insertions are reindentation of JSX that lost a wrapper.

### Deliberately not in scope

Flags authored by other people are untouched, even where they look similarly settled:

- `VITE_STUDIO_ENABLE_FLAT_INSPECTOR` / `VITE_STUDIO_FLAT_INSPECTOR_ENABLED` (default true, but not mine)
- `VITE_STUDIO_SDK_CUTOVER_ENABLED`, `VITE_STUDIO_SDK_CUTOVER_FAMILIES`, `VITE_STUDIO_SDK_RESOLVER_SHADOW_ENABLED` (SDK cutover canary, still soaking)
- `VITE_HYPERFRAMES_NO_TELEMETRY`

Mine but genuinely long-lived configuration rather than rollout gates, so they stay: `VITE_STUDIO_DISCOVERY_PORTS`, `VITE_HYPERFRAMES_FEEDBACK_INTERVAL`, `VITE_HYPERFRAMES_NO_FEEDBACK` (a documented user opt-out), plus the `HYPERFRAMES_*` binary paths, API URLs, cache sizes, and timeouts.

`VITE_STUDIO_ENABLE_MOTION_PANEL` / `VITE_STUDIO_MOTION_PANEL_ENABLED` were already retired from production code before this PR; they only survived as placeholder names inside the resolver's unit tests, and this PR swaps those out.

## Test plan

- [x] Unit tests added/updated - dropped the two tests asserting removed flag defaults; retargeted the `resolveStudioBooleanEnvFlag` cases at a live flag pair; updated `studioUrlState` tests for the narrowed `normalizeStudioUrlPanelTab` signature (now also asserts an unknown tab returns `null`).
- [x] Manual testing performed - see below.
- [ ] Documentation updated (if applicable) - not needed; no removed name appears in `docs/`, `skills/`, or `registry/`. (`docs/changelog.mdx` has one historical entry naming `STUDIO_KEYFRAMES_ENABLED`; changelog history is left as written.)

```
packages/studio: bunx vitest run          # 280 files, 3116 tests pass, 1 skipped
packages/studio: bunx tsc --noEmit        # clean
bun run build                             # green (all packages)
bunx oxlint  <25 changed files>           # 0 warnings, 0 errors
bunx oxfmt --check <25 changed files>     # clean
```

Two extra checks, because part of this diff was script-generated:

1. Zero references to any removed flag constant or env name remain anywhere outside `docs/changelog.mdx`.
2. Diffed every string literal in each changed non-test file against `origin/main`. The only differences are the intended removals: the 12 env names, `"Manual editing is temporarily disabled"`, the `"cursor-not-allowed …"` disabled class, the 3-column `"1fr 1fr 1fr"` grid, and the `"renders"` redirect literals. No user-facing label, tooltip, or class string changed by accident.

packages/studio/src/components/sidebar/LeftSidebar.tsx

@@ -12,7 +12,6 @@ import { AssetsTab } from "./AssetsTab";
 import { trackStudioEvent } from "../../utils/studioTelemetry";
 import { BlocksTab, type BlockPreviewInfo } from "./BlocksTab";
 import { FileTree } from "../editor/FileTree";
-import { STUDIO_BLOCKS_PANEL_ENABLED } from "../editor/manualEditingAvailability";
 import { Tooltip } from "../ui";
 
 export type SidebarTab = "compositions" | "assets" | "code" | "blocks";
@@ -127,11 +126,7 @@ export const LeftSidebar = memo(
               <div className="flex items-center gap-2">
                 <div
                   className="grid min-w-0 flex-1 gap-0.5 rounded-[18px] bg-neutral-900 p-1 shadow-[inset_0_1px_0_rgba(255,255,255,0.03)]"
-                  style={{
-                    gridTemplateColumns: STUDIO_BLOCKS_PANEL_ENABLED
-                      ? "1fr 1fr 1fr 1fr"
-                      : "1fr 1fr 1fr",
-                  }}
+                  style={{ gridTemplateColumns: "1fr 1fr 1fr 1fr" }}
                 >
                   <Tooltip label="Source code editor" side="bottom">
                     <button
@@ -172,21 +167,19 @@ export const LeftSidebar = memo(
                       Assets
                     </button>
                   </Tooltip>
-                  {STUDIO_BLOCKS_PANEL_ENABLED && (
-                    <Tooltip label="Browse blocks and components" side="bottom">
-                      <button
-                        type="button"
-                        onClick={() => selectTab("blocks")}
-                        className={`rounded-[14px] px-1.5 py-2 text-[10px] font-semibold truncate transition-all ${
-                          tab === "blocks"
-                            ? "bg-neutral-800 text-white"
-                            : "text-neutral-500 hover:text-neutral-200"
-                        }`}
-                      >
-                        Catalog
-                      </button>
-                    </Tooltip>
-                  )}
+                  <Tooltip label="Browse blocks and components" side="bottom">
+                    <button
+                      type="button"
+                      onClick={() => selectTab("blocks")}
+                      className={`rounded-[14px] px-1.5 py-2 text-[10px] font-semibold truncate transition-all ${
+                        tab === "blocks"
+                          ? "bg-neutral-800 text-white"
+                          : "text-neutral-500 hover:text-neutral-200"
+                      }`}
+                    >
+                      Catalog
+                    </button>
+                  </Tooltip>
                 </div>
                 {onToggleCollapse && (
                   <button
@@ -267,7 +260,7 @@ export const LeftSidebar = memo(
               </div>
             )}
 
-            {STUDIO_BLOCKS_PANEL_ENABLED && tab === "blocks" && (
+            {tab === "blocks" && (
               <BlocksTab onAddBlock={onAddBlock} onPreviewBlock={onPreviewBlock} />
             )}