Switch from Bifrost to LiteLLM; add Matrix channel; update rules

Infrastructure:
- docker-compose.yml: replace bifrost container with LiteLLM proxy
  (host.docker.internal:4000); complex model → deepseek-r1:free via
  OpenRouter; add Matrix URL env var; mount logs volume
- bifrost-config.json: add auth_config + postgres config_store (archived)

Routing:
- router.py: full semantic 3-tier classifier rewrite — nomic-embed-text
  centroids for light/medium/complex; regex pre-classifiers for all tiers;
  Russian utterance sets expanded
- agent.py: wire LiteLLM URL; add dry_run support; add Matrix channel

Channels:
- channels.py: add Matrix adapter (_matrix_send via mx- session prefix)

Rules / docs:
- agent-pipeline.md: remove /think prefix requirement; document automatic
  complex tier classification
- llm-inference.md: update BIFROST_URL → LITELLM_URL references; add
  remote model note for complex tier
- ARCHITECTURE.md: deleted (superseded by README.md)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

channels.py

@@ -49,6 +49,7 @@ async def deliver(session_id: str, channel: str, text: str) -> None:
 # ── built-in channel adapters ─────────────────────────────────────────────────
 
 GRAMMY_URL = os.getenv("GRAMMY_URL", "http://grammy:3001")
+MATRIX_URL = os.getenv("MATRIX_URL", "http://matrix:3002")
 
 
 async def _telegram_send(session_id: str, text: str) -> None:
@@ -64,12 +65,26 @@ async def _telegram_send(session_id: str, text: str) -> None:
             )
 
 
+async def _matrix_send(session_id: str, text: str) -> None:
+    """Send reply to Matrix via the matrix adapter POST /send endpoint."""
+    room_id = session_id.removeprefix("mx-")
+    MAX_MTX = 4000
+    chunks = [text[i:i + MAX_MTX] for i in range(0, len(text), MAX_MTX)]
+    async with httpx.AsyncClient(timeout=15) as client:
+        for chunk in chunks:
+            await client.post(
+                f"{MATRIX_URL}/send",
+                json={"room_id": room_id, "text": chunk},
+            )
+
+
 async def _cli_send(session_id: str, text: str) -> None:
     """CLI replies are handled entirely through the pending_replies queue — no-op here."""
     pass
 
 
 def register_defaults() -> None:
-    """Register the built-in Telegram and CLI channel adapters."""
+    """Register the built-in Telegram, Matrix, and CLI channel adapters."""
     register("telegram", _telegram_send)
+    register("matrix", _matrix_send)
     register("cli", _cli_send)