chore: bump TypeScript pins to ^6.0.3 across all 12 workspaces + thumbmarkjs 1.9 + add CLAUDE.md

Each workspace package was still pinning `typescript: ~5.5.x` or
`~5.8.2` in its own devDependencies even though the root bumped to 6.0.3
in 60b1143. The pins were dead (yarn 1 hoists from root) but they're
misleading when reading a single package.json. Bring them all to
`^6.0.3` to match the root.

Other:
- @thumbmarkjs/thumbmarkjs 1.8.1 → 1.9.0 (root + communication package)
- yarn.lock regenerated from a clean install (vitest 4 hoisting was
  flaking on the patch vite bump; reverted vite to ^8.0.10)

Adds CLAUDE.md at the repo root: short project context for future
sessions — stack, the 12-workspace layout, the React-friendly v2.1.0
additions (`subscribe()`, `subscribeMessage()`, snapshot getters), build
scripts, and known gotchas (`SessionDataManager.getUserData` does NOT
exist; sendChat* expects 3 args; dispatchEvent is sync).

package.json

@@ -31,7 +31,7 @@
   },
   "main": "./index",
   "dependencies": {
-    "@thumbmarkjs/thumbmarkjs": "^1.8.1",
+    "@thumbmarkjs/thumbmarkjs": "^1.9.0",
     "gifuct-js": "^2.1.2",
     "howler": "^2.2.4",
     "pako": "^2.1.0",