chore: rename quicproquo → quicprochat in Rust workspace

Rename all crate directories, package names, binary names, proto
package/module paths, ALPN strings, env var prefixes, config filenames,
mDNS service names, and plugin ABI symbols from quicproquo/qpq to
quicprochat/qpc.

sdks/ruby/lib/quicprochat/ffi_bindings.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require "ffi"
+
+module QuicProQuo
+  # Low-level FFI bindings to libquicproquo_ffi.
+  #
+  # The library is located via:
+  # 1. QPQ_LIB_PATH environment variable
+  # 2. Common cargo build output paths
+  # 3. System library path
+  module FFIBindings
+    extend FFI::Library
+
+    # Status codes (mirrors crates/quicproquo-ffi/src/lib.rs).
+    QPQ_OK            = 0
+    QPQ_ERROR         = 1
+    QPQ_AUTH_FAILED   = 2
+    QPQ_TIMEOUT       = 3
+    QPQ_NOT_CONNECTED = 4
+
+    # Locate and load the shared library.
+    LIB_SEARCH_PATHS = [
+      ENV.fetch("QPQ_LIB_PATH", nil),
+      File.expand_path("../../../../target/release/libquicproquo_ffi.so", __dir__),
+      File.expand_path("../../../../target/debug/libquicproquo_ffi.so", __dir__),
+      File.expand_path("../../../../target/release/libquicproquo_ffi.dylib", __dir__),
+      File.expand_path("../../../../target/debug/libquicproquo_ffi.dylib", __dir__),
+      "quicproquo_ffi",
+    ].compact.freeze
+
+    lib_path = LIB_SEARCH_PATHS.find { |p| File.exist?(p) } || "quicproquo_ffi"
+    ffi_lib lib_path
+
+    # QpqHandle* qpq_connect(const char*, const char*, const char*)
+    attach_function :qpq_connect, %i[string string string], :pointer
+
+    # int qpq_login(QpqHandle*, const char*, const char*)
+    attach_function :qpq_login, %i[pointer string string], :int
+
+    # int qpq_send(QpqHandle*, const char*, :pointer, size_t)
+    attach_function :qpq_send, %i[pointer string pointer size_t], :int
+
+    # int qpq_receive(QpqHandle*, uint32, :pointer)
+    attach_function :qpq_receive, %i[pointer uint32 pointer], :int
+
+    # void qpq_disconnect(QpqHandle*)
+    attach_function :qpq_disconnect, [:pointer], :void
+
+    # const char* qpq_last_error(const QpqHandle*)
+    attach_function :qpq_last_error, [:pointer], :string
+
+    # void qpq_free_string(char*)
+    attach_function :qpq_free_string, [:pointer], :void
+  end
+end