feat(tldraw): add headless RoomSnapshot to .tldr conversion

[steveruizok]

In order to turn a sync-worker RoomSnapshot JSON blob (as written to the R2 rooms-history-ephemeral bucket) into a standard .tldr file without spinning up a live Editor or touching the DOM, this PR adds a pure roomSnapshotToTldrawFile helper in the tldraw package plus a small tsx-based CLI in the sync-worker. Closes #8589.

The helper:

• Keeps only document-persistent record types (document, page, shape, asset, binding) and drops session-scoped records (instance, instance_page_state, instance_presence, camera, pointer, user).
• Prunes asset records that aren't referenced by a surviving shape.
• Uses type-only imports so it stays a zero-side-effect pure function — usable from Node scripts, CFW debugging tools, or anything else that has a snapshot in hand.

The CLI (apps/dotcom/sync-worker/scripts/snapshot-to-tldr.ts) reads a RoomSnapshot JSON from stdin or --in <path>, runs it through the helper, and writes the result to stdout or --out <path>. It imports the helper directly from its source file so we don't load the full tldraw package (React, editor, styles) just to transform JSON.

Asset URL rewriting / data-URI inlining is explicitly out of scope, since that needs a DOM or network. Consumers that want inlined assets can re-import the file into an editor and use the existing serializeTldrawJson path.

API changes

• Added roomSnapshotToTldrawFile(snapshot) — pure conversion from a RoomSnapshot-shaped input to a TldrawFile.
• Added RoomSnapshotLike interface — a structural mirror of @tldraw/sync-core's RoomSnapshot, used as the helper's input type so that tldraw does not need to depend on sync-core. Any real RoomSnapshot is structurally assignable to it.

Change type

• feature

Test plan

1. Pipe a real bucket snapshot JSON through the CLI:

   yarn tsx apps/dotcom/sync-worker/scripts/snapshot-to-tldr.ts --in snapshot.json --out room.tldr
   

2. Open the resulting .tldr in the tldraw editor (yarn dev, File → Open). Confirm shapes, pages, and bindings load with no parse errors.

• Unit tests

Release notes

• Add roomSnapshotToTldrawFile, a pure helper that converts a sync RoomSnapshot JSON blob into a .tldr-compatible TldrawFile without needing a live editor or DOM.

Code changes

Section	LOC change
Core code	+65 / -0
Tests	+159 / -0
Automated files	+22 / -0
Apps	+59 / -0

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[steveruizok]

@copilot review

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[Copilot]

@copilot review

Self-review done. Found and fixed the main issue: duplicated pruneUnusedAssets logic between file.ts and roomSnapshotToTldrawFile.ts. Now pruneUnusedAssets is exported as @internal from file.ts and reused in the new helper. See commit c60f040.