project: widen prettier scope to cover all files

Switch format scripts from explicit path lists to `prettier .`
(matching ably-js's approach). Submodules (ably-common, specification)
are excluded via .prettierignore.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mschristensen

.prettierignore

@@ -0,0 +1,2 @@
+ably-common/
+specification/

package.json

@@ -46,8 +46,8 @@
     "prepare": "npm run build",
     "lint": "eslint .",
     "lint:fix": "eslint --fix .; (npm run format > /dev/null)",
-    "format": "prettier --list-different --write src demo/vercel/react/*/src",
-    "format:check": "prettier --check src demo/vercel/react/*/src",
+    "format": "prettier --list-different --write .",
+    "format:check": "prettier --check .",
     "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:integration": "vitest run --config vitest.config.integration.ts",