docs(kits): add machine-readable deprecation markers to kit READMEs

[cabljac]

Summary

Adds a machine-readable deprecation marker plus a visible deprecation notice to the top of each kit README on the kits branch. A scraping script can pick up the HTML comment to power CLI warnings and migration nudges for users of the deprecated extensions.

Marker format:

<!-- FIREBASE_EXTENSION_REPLACEMENT: extension="firebase/firestore-send-email" package="@firebase/firestore-send-email" -->

> **Deprecation Notice:** The Firebase Extension `firebase/firestore-send-email` is deprecated. Please migrate to the [`@firebase/firestore-send-email`](https://www.npmjs.com/package/@firebase/firestore-send-email) package.

The marker includes an extension= field alongside package= so the scraper does not need to infer the extension ID from the repo path. This matters because publishers differ across kits:

Kit	Deprecated extension	Replacement package
firestore-bigquery-export	firebase/firestore-bigquery-export	@firebase/firestore-bigquery-export
firestore-counter	firebase/firestore-counter	@firebase/firestore-counter
firestore-genai-chatbot	googlecloud/firestore-genai-chatbot	@firebase/firestore-genai-chatbot
firestore-incremental-capture	googlecloud/firestore-incremental-capture	@firebase/firestore-incremental-capture
firestore-send-email	firebase/firestore-send-email	@firebase/firestore-send-email
firestore-translate-text	firebase/firestore-translate-text	@firebase/firestore-translate-text
rtdb-limit-child-nodes	firebase/rtdb-limit-child-nodes	@firebase/rtdb-limit-child-nodes
speech-to-text	googlecloud/speech-to-text	@firebase/speech-to-text

Notes

• Several kits (firestore-counter, firestore-genai-chatbot, firestore-incremental-capture, firestore-translate-text) are still skeletons. Their markers are included so the scraper can be tested end to end, but the npm package links will not resolve until those packages are published.
• Draft until the marker format is agreed with the scraper side.

[gemini-code-assist]

Code Review

This pull request adds deprecation notices and replacement HTML comments to the README files of several Firebase extension kits. The reviewer suggested wrapping the attribute values in the HTML comments in double quotes to ensure robust parsing and standard formatting.

[cabljac]

Applied the quoting suggestion to all 8 READMEs.

Also fixed the two CI failures, both pre-existing on the kits branch (from the recently added storage-resize-images and firestore-vector-search kits, not the README changes):

• formatting: prettier 2.7.1 cannot parse the TS satisfies operator used in the new kits. Bumped to 2.8.8 (minimal version that supports it) and reformatted the two files it flags.
• license: ran scripts/addlicense.sh fix to add missing Apache headers to 41 files in the new kits.

[ajperel]

You acted very quickly, but unfortunately what you were told in chat is wrong. We don't need the markup on extension replacement in kits README files. The must be in the extension source files, e.g., the readme that you'd see if you follow the "source code" link from an Extension page like: https://extensions.dev/extensions/firebase/firestore-bigquery-export

[cabljac]

Follow-ups: markers moved to the extension READMEs in #2935 (via PREINSTALL.md since READMEs are generated), and the kit-side markers are removed in #2936.