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/components/editor/MotionPanelFields.tsx

@@ -1,7 +1,7 @@
 import { useState, useRef, useEffect, type ReactNode } from "react";
 import { Zap } from "../../icons/SystemIcons";
 
-export const FIELD =
+const FIELD =
   "min-w-0 rounded-xl border border-neutral-800 bg-neutral-900/95 px-3 py-2 text-neutral-100 shadow-[inset_0_1px_0_rgba(255,255,255,0.03)] transition-colors focus-within:border-neutral-600";
 export const LABEL = "text-[11px] font-medium uppercase tracking-[0.18em] text-neutral-500";
 export const RESPONSIVE_GRID = "grid grid-cols-[repeat(auto-fit,minmax(118px,1fr))] gap-3";
@@ -30,7 +30,7 @@ export function parsePlainNumber(value: string): number | null {
 
 // ── CommitField ──
 
-export function CommitField({
+function CommitField({
   value,
   disabled,
   onCommit,