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/producer/src/services/compilationTester.ts

@@ -39,7 +39,7 @@ const EPSILON = 0.001; // Tolerance for floating-point timing comparisons
  * Parse HTML and extract all elements with timing attributes.
  * Includes <video>, <audio>, and <div data-composition-src>.
  */
-export function extractTimedElements(html: string): CompiledElement[] {
+function extractTimedElements(html: string): CompiledElement[] {
   const elements: CompiledElement[] = [];
 
   // Extract video elements

packages/producer/src/services/distributed/shared.ts

@@ -73,7 +73,7 @@ export async function readFfmpegVersion(): Promise<string> {
 }
 
 /** Test-only: clear the cached ffmpeg version so a fresh probe runs. */
-export function _resetFfmpegVersionCacheForTests(): void {
+function _resetFfmpegVersionCacheForTests(): void {
   cachedFfmpegVersion = null;
 }
 

packages/producer/src/services/fileServer.ts

@@ -15,7 +15,7 @@ import { join, extname, resolve, sep } from "node:path";
 import { injectScriptsAtHeadStart, injectScriptsIntoHtml } from "@hyperframes/core/compiler";
 import { getVerifiedHyperframeRuntimeSource } from "./hyperframeRuntimeLoader.js";
 
-export { injectScriptsAtHeadStart, injectScriptsIntoHtml };
+export { injectScriptsAtHeadStart };
 
 type PathModuleLike = {
   resolve: (...segments: string[]) => string;

packages/producer/src/services/render/stages/freezePlan.ts

@@ -116,7 +116,6 @@ export interface FreezePlanResult {
  * `../runtimeEnvSnapshot.ts` — chunk workers re-apply the snapshot during
  * boot, so it needs to be importable without dragging in the freeze pipeline.
  */
-export { RUNTIME_ENV_PREFIXES, snapshotRuntimeEnv } from "../runtimeEnvSnapshot.js";
 
 /** The relative path inside `<planDir>/` to the compiled HTML. */
 const COMPILED_INDEX_RELATIVE_PATH = "compiled/index.html";