Remove legacy `@cipherstash/drizzle` package before Stack 1.0

[coderdan]

Summary

@cipherstash/protect is sunsetting at Stack 1.0, and @cipherstash/drizzle is its Drizzle integration — a ~645-line-diverged fork of what became @cipherstash/stack-drizzle, in maintenance-by-attrition since the adapter split. Keeping it on the release train has two live costs:

1. Every rc republishes known-buggy code unreviewed — 3.0.4-rc.1 shipped with perf: legacy @cipherstash/drizzle has the same bare-equality bug as @cipherstash/stack/drizzle #426 (bare-equality bypasses hmac functional indexes) still open against it.
2. Name hazard at 1.0 — npm install @cipherstash/drizzle looks like the obvious command, works, and silently binds new users (and LLM assistants) to the predecessor SDK. It currently out-downloads its successor (~341/wk vs ~204/wk for stack-drizzle). Same stale-package hazard class as npm dist-tags deliver broken/stale packages: adapters' latest=0.0.0, stack latest=0.19.0; stash init installs unpinned #661.

Expected

• Delete packages/drizzle (git history is the maintenance branch; npm keeps published versions installable forever).
• Keep Changesets pre-release state consistent so the rc.2 Version Packages run doesn't trip on a missing package.
• Remove its CI/workflow entries (tests.yml .env scaffolds, Bun test-loop entry, rebuild-docs tag trigger) and the unused e2e dep.
• Keep meta files honest (AGENTS.md Repository Layout, SECURITY.md package table).
• State the deprecation where users read it (skills/stash-drizzle/SKILL.md, @cipherstash/stack-drizzle README).

Registry follow-up (npm owner, after merge)

npm deprecate @cipherstash/drizzle "Deprecated: @cipherstash/protect is sunsetting at Stack 1.0. Use @cipherstash/stack-drizzle with @cipherstash/stack."

Resolution

Done in #667 — package deleted, changesets/CI/meta/docs updated.

[coderdan]

Resolved by #667 (merged).