feat: MCP (Model Context Protocol) server

- POST /mcp (JSON-RPC 2.0): initialize, ping, tools/list, tools/call; notifications -> 202
- tools: cortiq_route (classify -> routing decision) and cortiq_chat (route -> answer)
- gated by protocols.mcp; admin meta marks it implemented
- docs: README/README.ru protocol tables, highlights and status updated for
  streaming, Anthropic, embeddings, semantic cache and MCP

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/protocols/mod.rs

@@ -2,6 +2,7 @@
 //! its protocol to/from the canonical model. Enabled via flags in `[protocols]`.
 
 pub mod anthropic_messages;
+pub mod mcp;
 pub mod openai_chat;
 pub mod openai_embeddings;
 
@@ -16,5 +17,6 @@ pub fn build_router() -> Router<SharedState> {
         .merge(openai_chat::routes())
         .merge(openai_embeddings::routes())
         .merge(anthropic_messages::routes())
-    // TODO: openai_completions, openai_models, mcp, native_passthrough.
+        .merge(mcp::routes())
+    // TODO: openai_completions, openai_models, native_passthrough.
 }