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/player/lib/playbackAdapter.ts

@@ -20,7 +20,7 @@ export function isFinitePositive(value: number): boolean {
   return Number.isFinite(value) && value > 0;
 }
 
-export function clampTime(time: number, duration: number): number {
+function clampTime(time: number, duration: number): number {
   const safeDuration = Math.max(0, Number.isFinite(duration) ? duration : 0);
   const safeTime = Math.max(0, Number.isFinite(time) ? time : 0);
   return safeDuration > 0 ? Math.min(safeTime, safeDuration) : safeTime;

packages/studio/src/player/lib/timelineElementHelpers.ts

@@ -15,7 +15,7 @@ import { isFinitePositive } from "./playbackAdapter";
 // Duration attribute helpers
 // ---------------------------------------------------------------------------
 
-export function readDurationAttribute(el: Element | null | undefined): number {
+function readDurationAttribute(el: Element | null | undefined): number {
   if (!el) return 0;
   const duration =
     Number.parseFloat(el.getAttribute("data-duration") ?? "") ||
@@ -42,7 +42,7 @@ export function readTimelineDurationFromDocument(doc: Document | null | undefine
 // DOM element type guards
 // ---------------------------------------------------------------------------
 
-export function isHtmlElement(el: Element): el is HTMLElement {
+function isHtmlElement(el: Element): el is HTMLElement {
   const HtmlElementCtor = el.ownerDocument.defaultView?.HTMLElement ?? globalThis.HTMLElement;
   return typeof HtmlElementCtor !== "undefined" && el instanceof HtmlElementCtor;
 }
@@ -113,7 +113,7 @@ export function getTimelineElementDisplayLabel(input: {
   return tag ? `${tag} clip` : "Timeline clip";
 }
 
-export const IMPLICIT_TIMELINE_LAYER_SKIP_TAGS = new Set([
+const IMPLICIT_TIMELINE_LAYER_SKIP_TAGS = new Set([
   "base",
   "link",
   "meta",
@@ -123,7 +123,7 @@ export const IMPLICIT_TIMELINE_LAYER_SKIP_TAGS = new Set([
   "template",
 ]);
 
-export function humanizeTimelineIdentifier(value: string): string {
+function humanizeTimelineIdentifier(value: string): string {
   return value
     .trim()
     .replace(/[_-]+/g, " ")
@@ -239,7 +239,7 @@ export function getTimelineElementIdentity(element: TimelineElement): string {
 // DOM node querying
 // ---------------------------------------------------------------------------
 
-export function getTimelineDomNodes(doc: Document): Element[] {
+function getTimelineDomNodes(doc: Document): Element[] {
   const rootComp = doc.querySelector("[data-composition-id]");
   return Array.from(doc.querySelectorAll("[data-start]")).filter((node) => node !== rootComp);
 }