chore: realign .claude config to the Optia extension (audit results)

Replace leftover Figma-to-React framework tooling with config that actually describes this MV3 Chrome extension.

- Rewrite CLAUDE.md: real commands (cd app; dual dev modes), architecture map, SEO scoring model, testing + release notes, and a 'does NOT use' list.

- Add project skills: chrome-extension-dev (MV3 message/storage/SW lifecycle contracts) and testing-chrome-extension (real Vitest/chrome-mock/openai-mock patterns).

- Add commands: /release-extension (version sync + store checklist) and /add-seo-check (the cross-file contract). Fix /lint (ESLint-only, no Prettier) and /test (Vitest-only, run from app/).

- Fix .mcp.json drift: drop the Figma servers (they inject 'use Figma' prompts), declare chrome-devtools (the MCP actually used).

- Replace the broken PostToolUse hook with .claude/hooks/guards.mjs: blocks root releases, reminds on extractor-twin and manifest version/permission edits.

- Prune 30 irrelevant agents (keep 14), the 9 Figma/React skills, dead commands, scripts/ + templates/ scaffolding, Figma/React docs, and the root release config.

Based on a multi-agent audit of the repo. No app/ code changes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Paul Mulligan