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- ARCHITECTURE.md: deleted (superseded by README.md)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>

bifrost-config.json

@@ -1,4 +1,21 @@
 {
+  "auth_config": {
+    "is_enabled": true,
+    "admin_username": "admin",
+    "admin_password": "env.BIFROST_ADMIN_PASSWORD"
+  },
+  "config_store": {
+    "enabled": true,
+    "type": "postgres",
+    "config": {
+      "host": "bifrost-db",
+      "port": "5432",
+      "user": "bifrost",
+      "password": "bifrost",
+      "db_name": "bifrost",
+      "ssl_mode": "disable"
+    }
+  },
   "client": {
     "drop_excess_requests": false
   },