refactor: drop unused exports detected by fallow auto-fix

Run `fallow fix --auto-fixable` to remove `export` keywords from symbols
fallow's reachability analysis identifies as unused. Keeps only the cases
where the symbol is still referenced internally in its own file (so
removing `export` doesn't surface a new oxlint `no-unused-vars` error).

Result: fallow dead-code findings drop from 276 → 208 (68 fewer unused
exports), with no behavior change — each symbol is still defined and used
exactly the same way within its file.

Reverted ~20 files where fallow's auto-fix would have created cascading
"declared but never used" lint errors — those are cases where the symbol
isn't used at all, and properly cleaning them up means deleting the
declaration, not just dropping `export`. Better to land that as a
separate, narrower PR rather than mixing it into a mechanical de-export.

Also reverted four false positives where fallow missed real consumers:
- `captureCost.ts` (renderOrchestrator has two separate import blocks
  from the same module; fallow only saw the first)
- `propertyPanelHelpers.ts`, `domEditingLayers.ts` (real internal uses
  fallow's reachability missed)
- `render.ts` (functions imported via `await import()` dynamic import,
  which fallow's static analysis doesn't follow)

Test plan: bun run --filter '*' typecheck (clean), oxlint + oxfmt clean,
cli/core/studio/engine vitest suites pass (335 + 917 + 576 + 605 tests).

packages/studio/src/utils/studioFontHelpers.ts

@@ -22,7 +22,7 @@ const GENERIC_FONT_FAMILIES = new Set([
   "fangsong",
 ]);
 
-export function primaryFontFamilyFromCss(value: string): string {
+function primaryFontFamilyFromCss(value: string): string {
   const first = value.split(",")[0] ?? "";
   return first.trim().replace(/^["']|["']$/g, "");
 }

packages/studio/src/utils/studioUrlState.ts

@@ -80,7 +80,7 @@ function normalizeSelection(params: URLSearchParams): StudioUrlSelectionState |
   };
 }
 
-export function defaultStudioUrlState(): StudioUrlState {
+function defaultStudioUrlState(): StudioUrlState {
   return {
     activeCompPath: null,
     currentTime: null,

packages/studio/src/utils/timelineInspector.ts

@@ -1,6 +1,6 @@
 import type { TimelineElement } from "../player";
 
-export const TIMELINE_INSPECTOR_BOUNDARY_EPSILON_SECONDS = 0.08;
+const TIMELINE_INSPECTOR_BOUNDARY_EPSILON_SECONDS = 0.08;
 
 const AUDIO_TIMELINE_TAGS = new Set(["audio", "music", "sfx", "sound", "narration"]);
 const AUDIO_SOURCE_EXT_RE = /\.(aac|flac|m4a|mp3|ogg|opus|wav)(?:[?#].*)?$/i;