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-python/pyproject.toml

@@ -0,0 +1,17 @@
+[build-system]
+requires      = ["maturin>=1.0,<2.0"]
+build-backend = "maturin"
+
+[project]
+name            = "quicnprotochat"
+version         = "0.1.0"
+description     = "Python bindings for quicnprotochat — QUIC + MLS + post-quantum E2E chat."
+license         = { text = "MIT" }
+requires-python = ">=3.8"
+readme          = "README.md"
+
+[tool.maturin]
+# The Cargo manifest is one level up in the workspace; point maturin at it.
+manifest-path = "Cargo.toml"
+module-name   = "quicnprotochat"
+features      = ["pyo3/extension-module"]