feat(dotcom): update default welcome template content (tldraw#9272)

In order to refresh the content new tldraw.com workspaces are seeded
with, this PR re-exports the committed default welcome snapshot from the
staging "workspace template" board. The new canvas is a workspace
onboarding walkthrough — creating a workspace, what a workspace is,
inviting your team with an invite link, moving files into a workspace,
pinning files, and managing members (roles, removing people) — replacing
the previous three-panel comic.

This default is only used for a fresh workspace's first file when no
file has been marked as the welcome template (fresh dev/preview/prod).
Once an admin marks a welcome-template file, its published snapshot
supersedes this default.

The snapshot is the baked JSON of a `RoomSnapshot`, exported via
`editor.store.serialize('document')` and scrubbed of authoring identity
(no `user` records). The first-viewport bounds check in
`welcome.test.ts` is widened (`x < 1550`, `y < 1050`) to fit the new
design's larger extent, since new files open at the default camera with
no zoom-to-fit.

### Change type

- [x] `improvement`

### Test plan

1. On a fresh workspace (no welcome template marked), create a new file
and confirm it opens seeded with the new onboarding board, content
visible at the default camera.

- [x] Unit tests

### Code changes

| Section         | LOC change   |
| --------------- | ------------ |
| Tests           | +2 / -2      |
| Apps            | +4308 / -997 |

### Release notes

- Update the default welcome content new tldraw.com workspaces are
seeded with.

Author: jsscclr

apps/dotcom/sync-worker/package.json

@@ -17,7 +17,7 @@
 		"test": "yarn run -T vitest --passWithNoTests",
 		"clean": "rm -rf .wrangler/state .wrangler/state-*",
 		"test-coverage": "yarn run -T vitest run --coverage --passWithNoTests",
-		"check-bundle-size": "yarn run -T tsx ../../../internal/scripts/check-worker-bundle.ts --entry src/worker.ts --size-limit-bytes 1500000",
+		"check-bundle-size": "yarn run -T tsx ../../../internal/scripts/check-worker-bundle.ts --entry src/worker.ts --size-limit-bytes 1600000",
 		"reset-db": "./reset-db.sh",
 		"lint": "yarn run -T tsx ../../../internal/scripts/lint.ts"
 	},