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-ruby/Rakefile

@@ -0,0 +1,39 @@
+require "fileutils"
+
+WORKSPACE_ROOT = File.expand_path("../..", __dir__)
+TARGET_DIR     = File.join(WORKSPACE_ROOT, "target")
+LIB_DIR        = File.join(__dir__, "lib")
+
+# Detect the shared library extension for the current platform.
+SO_EXT = case RUBY_PLATFORM
+         when /darwin/ then "dylib"
+         when /mingw|mswin/ then "dll"
+         else "so"
+         end
+
+LIB_SRC  = File.join(TARGET_DIR, "release", "libquicnprotochat_ruby.#{SO_EXT}")
+LIB_DEST = File.join(LIB_DIR, "quicnprotochat_ruby.#{SO_EXT}")
+
+desc "Build the native extension (release)"
+task :build do
+  sh "cargo build --release --manifest-path #{File.join(__dir__, "Cargo.toml")}"
+  FileUtils.mkdir_p(LIB_DIR)
+  FileUtils.cp(LIB_SRC, LIB_DEST)
+  puts "Copied #{LIB_DEST}"
+end
+
+desc "Build the native extension (debug)"
+task :build_dev do
+  sh "cargo build --manifest-path #{File.join(__dir__, "Cargo.toml")}"
+  lib_src = File.join(TARGET_DIR, "debug", "libquicnprotochat_ruby.#{SO_EXT}")
+  FileUtils.mkdir_p(LIB_DIR)
+  FileUtils.cp(lib_src, LIB_DEST)
+  puts "Copied #{LIB_DEST} (debug)"
+end
+
+desc "Remove build artefacts"
+task :clean do
+  FileUtils.rm_f(LIB_DEST)
+end
+
+task default: :build