docs: add CLAUDE.md for Claude Code quick reference (#5683)

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

CLAUDE.md

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+# CLAUDE.md
+
+Memos — self-hosted knowledge management platform. Go 1.25 backend, React 18 + TypeScript + Vite 7 frontend, Protocol Buffers API.
+
+See `AGENTS.md` for full architecture, workflows, and patterns.
+
+## Essential Commands
+
+### Backend
+
+```bash
+go run ./cmd/memos --port 8081    # Start dev server
+go test ./...                      # Run all tests
+golangci-lint run                  # Lint
+goimports -w .                     # Format imports
+```
+
+### Frontend
+
+```bash
+cd web && pnpm install             # Install deps
+pnpm dev                           # Dev server (proxies to :8081)
+pnpm lint                          # Type check + Biome lint
+pnpm lint:fix                      # Auto-fix lint issues
+pnpm format                        # Format code
+pnpm build                         # Production build
+```
+
+### Protocol Buffers
+
+```bash
+cd proto && buf generate            # Regenerate Go + TypeScript
+cd proto && buf lint                # Lint proto files
+```
+
+## Key Rules
+
+- **Go errors:** Use `errors.Wrap(err, "context")` from `github.com/pkg/errors`. Never use `fmt.Errorf`.
+- **Go imports:** stdlib → third-party → local (`github.com/usememos/memos`). Run `goimports -w .`.
+- **Go comments:** All exported functions must have doc comments (godot enforced).
+- **Go gRPC errors:** Return `status.Errorf(codes.X, "message")` from service methods.
+- **Frontend imports:** Use `@/` alias for absolute imports.
+- **Frontend formatting:** Biome — 140 char lines, double quotes, always semicolons, 2-space indent.
+- **Frontend state:** Server data via React Query hooks (`web/src/hooks/`). Client state via React Context.
+- **Database changes:** Must provide migration files for all 3 drivers (sqlite, mysql, postgres) and update `LATEST.sql`.
+- **Proto changes:** Run `buf generate` after editing `.proto` files. Generated code is in `proto/gen/` and `web/src/types/proto/`.
+- **Public endpoints:** Add to `server/router/api/v1/acl_config.go`.