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.

crates/quicnprotochat-bindings/Cargo.toml

@@ -0,0 +1,47 @@
+[package]
+name        = "quicnprotochat-bindings"
+version     = "0.1.0"
+edition     = "2021"
+description = "Language-agnostic Rust library powering Python and Ruby native bindings."
+license     = "MIT"
+
+[lib]
+name       = "quicnprotochat_bindings"
+crate-type = ["rlib"]
+
+[dependencies]
+quicnprotochat-core  = { git = "git@git.xorwell.de:c/quicnprotochat.git" }
+quicnprotochat-proto = { git = "git@git.xorwell.de:c/quicnprotochat.git" }
+openmls_rust_crypto  = { workspace = true }
+
+# Serialisation + RPC
+capnp     = { workspace = true }
+capnp-rpc = { workspace = true }
+
+# Async / networking
+tokio      = { workspace = true }
+tokio-util = { workspace = true }
+futures    = { workspace = true }
+quinn      = { workspace = true }
+quinn-proto = { workspace = true }
+rustls     = { workspace = true }
+
+# Serialisation
+serde   = { workspace = true }
+bincode = { workspace = true }
+
+# Crypto — OPAQUE PAKE
+opaque-ke = { workspace = true }
+rand      = { workspace = true }
+
+# State encryption
+argon2           = { workspace = true }
+chacha20poly1305 = { workspace = true }
+sha2             = { workspace = true }
+
+# Error handling
+anyhow    = { workspace = true }
+thiserror = { workspace = true }
+
+# Hex encoding for public return values
+hex = "0.4"