docs: add CLAUDE.md, unignore from .gitignore

CLAUDE.md

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+# product.quicproquo
+
+End-to-end encrypted group messaging over QUIC with MLS key agreement and post-quantum crypto.
+
+## Tech Stack
+
+- Rust 1.75+, Cargo workspace (12 crates)
+- Crypto: OpenMLS 0.8, ML-KEM-768, X25519, ChaCha20-Poly1305, OPAQUE-KE
+- Networking: Quinn (QUIC), Tokio, Tower middleware
+- Serialization: Protobuf (prost) for v2, Cap'n Proto (legacy v1)
+- DB: rusqlite with bundled SQLCipher
+- Build: just (justfile), cargo-deny for supply chain audit
+
+## Commands
+
+```bash
+just build              # Build all workspace crates
+just test               # Run all tests
+just test-core          # Crypto tests only
+just lint               # clippy --workspace -- -D warnings
+just fmt                # Format check
+just fmt-fix            # Format fix
+just proto              # Rebuild protobuf codegen
+just server             # Build server binary
+just client             # Build client binary
+cargo deny check        # Supply chain audit (deny.toml)
+```
+
+## Architecture
+
+```
+crates/
+  quicprochat-core/        # Crypto primitives, MLS, double ratchet
+  quicprochat-proto/       # Protobuf definitions + prost codegen
+  quicprochat-rpc/         # RPC framework over QUIC
+  quicprochat-sdk/         # High-level client SDK
+  quicprochat-server/      # Server binary
+  quicprochat-client/      # CLI client binary
+  quicprochat-p2p/         # P2P mesh via iroh (feature-gated: `mesh`)
+  quicprochat-plugin-api/  # Plugin interface
+  quicprochat-kt/          # Kotlin/JNI bindings
+  meshservice/             # Generic decentralized service layer (FAPP, Housing)
+apps/gui/                  # GUI application
+proto/                     # .proto source files
+schemas/                   # Data schemas
+docker/                    # Container configs
+```
+
+## Rules
+
+- `clippy::unwrap_used` is **deny** workspace-wide -- use proper error handling
+- `unsafe_code` is **warn** -- avoid unless absolutely necessary, document why
+- P2P crate (`quicprochat-p2p`) pulls ~90 extra deps via iroh -- only compiled with `mesh` feature
+- All crypto operations must go through quicprochat-core, never inline crypto
+- Protobuf is the v2 wire format; Cap'n Proto is legacy v1 only
+
+## Do NOT
+
+- Use `.unwrap()` or `.expect()` outside tests -- clippy will deny it
+- Add crypto primitives outside of quicprochat-core
+- Enable the `mesh` feature by default (heavy dependency tree)
+- Mix v1 (capnp) and v2 (protobuf) serialization in new code
+- Skip `cargo deny check` before adding new dependencies