feat: add Python (PyO3) and Ruby (Magnus) native bindings

Introduces three crates:
- quicnprotochat-bindings: shared Rust API returning structured data
  instead of printing to stdout; explicit per-call auth (no global
  OnceLock); QPCE state files fully interoperable with the CLI.
- quicnprotochat-python: PyO3 0.22 extension; GIL released during
  all blocking QUIC calls via py.allow_threads.
- quicnprotochat-ruby: Magnus 0.7 extension; Rakefile build task.

Core/proto crates referenced via git dep on the main repo.

Cargo.toml

@@ -0,0 +1,44 @@
+[workspace]
+resolver = "2"
+members = [
+    "crates/quicnprotochat-bindings",
+    "crates/quicnprotochat-python",
+    "crates/quicnprotochat-ruby",
+]
+
+# ── Shared dependency versions ────────────────────────────────────────────────
+[workspace.dependencies]
+# ── Crypto ───────────────────────────────────────────────────────────────────
+openmls             = { version = "0.5", default-features = false, features = ["crypto-subtle"] }
+openmls_rust_crypto = { version = "0.2" }
+openmls_traits      = { version = "0.2" }
+tls_codec           = { version = "0.3", features = ["derive"] }
+ml-kem              = { version = "0.2" }
+x25519-dalek        = { version = "2", features = ["static_secrets"] }
+ed25519-dalek       = { version = "2", features = ["rand_core"] }
+sha2                = { version = "0.10" }
+hkdf                = { version = "0.12" }
+chacha20poly1305    = { version = "0.10" }
+opaque-ke           = { version = "4", features = ["ristretto255", "argon2"] }
+zeroize             = { version = "1", features = ["derive", "serde"] }
+subtle              = { version = "2" }
+argon2              = { version = "0.5" }
+rand                = { version = "0.8" }
+serde               = { version = "1", features = ["derive"] }
+bincode             = { version = "1" }
+
+# ── Serialisation + RPC ───────────────────────────────────────────────────────
+capnp     = { version = "0.19" }
+capnp-rpc = { version = "0.19" }
+
+# ── Async / networking ────────────────────────────────────────────────────────
+tokio      = { version = "1", features = ["full"] }
+tokio-util = { version = "0.7", features = ["codec", "compat"] }
+futures    = { version = "0.3" }
+quinn      = { version = "0.11" }
+quinn-proto = { version = "0.11" }
+rustls     = { version = "0.23", default-features = false, features = ["std", "ring"] }
+
+# ── Error handling ────────────────────────────────────────────────────────────
+anyhow    = { version = "1" }
+thiserror = { version = "1" }