docs: update CLAUDE.md and remove AGENTS.md (#854)

Consolidate AGENTS.md into CLAUDE.md with enhanced guidance:
- Add post-task checklist requiring changelog and docs updates
- Add auth headers reference
- Add squash merge convention

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

AGENTS.md

@@ -1,35 +0,0 @@
-# Repository Guidelines
-
-## Project Structure
-- Backend: `worker/` (Workers API; entry `worker/src/worker.ts`, APIs under `worker/src/*_api/`).
-- Frontend: `frontend/` (Vue 3 app; routes in `frontend/src/router/`).
-- Pages middleware: `pages/functions/_middleware.js`.
-- Mail parser: `mail-parser-wasm/` (Rust WASM).
-- SMTP/IMAP proxy: `smtp_proxy_server/`.
-- DB schema/migrations: `db/`.
-- Docs: `vitepress-docs/`.
-
-## Build & Dev Commands
-Run inside each folder:
-- Frontend: `pnpm dev`, `pnpm build`.
-- Worker: `pnpm dev`, `pnpm lint`, `pnpm build`.
-- Pages: `pnpm dev`.
-- Docs: `pnpm dev` in `vitepress-docs/`.
-- WASM: `wasm-pack build --release` in `mail-parser-wasm/`.
-- SMTP proxy: `pip install -r smtp_proxy_server/requirements.txt` then `python smtp_proxy_server/main.py`.
-
-## Coding Style
-- Follow existing module style. `worker/` uses TypeScript + ESLint; `frontend/` uses Vue SFCs.
-- Keep current naming patterns: `*_api/`, `utils/`, `models/`.
-- ESM imports only (`type: module`).
-
-## Testing
-- No formal test runner. Validate with local dev servers and key flows (login, inbox, send/receive).
-
-## Commits & PRs
-- Use Conventional Commits (`feat:`, `fix:`, `docs:`). Recent history includes PR numbers like `(#123)`.
-- PRs should explain scope and add screenshots for UI changes.
-
-## Config Tips
-- Worker settings in `worker/wrangler.toml` (see template for bindings).
-- Frontend uses `VITE_*` env vars. Don’t commit secrets.