docs: add SAIA rate limits, Bifrost governance, and admin auth notes to mcp-gateway.md

- SAIA rate limits: minute=30/1m active at provider level; hour/day rows exist but not linked
- VK governance: allow_all_keys SQL workaround, allowed_models must be non-null JSON text
- Fix stale sk-tapirnase reference in add-MCP-client example (now uses cookie auth)
- Add LLM provider table

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

services/mcp-gateway.md

@@ -88,6 +88,55 @@ Settings → Integrations → Add MCP server:
 - URL: `https://ai.nuclide.systems/mcp`
 - Header: `Authorization: Bearer sk-bf-279d3ecc-9031-41ff-a582-ecf3dca61d52`
 
+## LLM Inference & Governance
+
+Bifrost proxies LLM inference at `/v1` (OpenAI-compatible). `enforce_auth_on_inference=1` — all `/v1` calls require a valid `sk-bf-*` VK.
+
+### Providers
+
+| Provider | Internal name | Base URL | Notes |
+|---|---|---|---|
+| SAIA (GPU cluster) | `openai` | `https://chat-ai.academiccloud.de/v1` | Rate limited (see below) |
+| Google Gemini | `gemini` | default | |
+| Mistral AI | `mistral` | default | |
+| Cerebras | `cerebras` | default | |
+| claude-max-bridge | `openrouter` | `http://claude-max-bridge:8000` | Claude Opus/Sonnet/Haiku via max subscription |
+
+### SAIA rate limits
+
+SAIA enforces per-account quotas. Bifrost is configured with a global provider-level limit (`config_providers.rate_limit_id='saia-minute'`):
+
+| Window | SAIA limit | Bifrost enforcement |
+|---|---|---|
+| Per minute | 30 req | ✅ active (`saia-minute` row) |
+| Per hour | 200 req | row exists (`saia-hour`), not linked |
+| Per day | 1000 req | row exists (`saia-day`), not linked |
+| Per month | 3000 req | not trackable across restarts |
+
+**Note**: Bifrost only supports one rate limit window per provider. The minute window is linked because it provides burst protection. The `saia-hour` / `saia-day` rows are in `governance_rate_limits` and can be linked by updating `config_providers SET rate_limit_id='saia-hour'` if needed.
+
+To change the active window:
+```bash
+sqlite3 /opt/stacks/ai/bifrost/data/config.db \
+  "UPDATE config_providers SET rate_limit_id='saia-day' WHERE name='openai';"
+docker compose -f /opt/stacks/ai/bifrost.yml up -d --force-recreate
+```
+
+**Rate limit API**: `GET /api/governance/rate-limits` is read-only. POST/PUT return 405. Use direct SQLite to create new entries.
+
+### Virtual key governance
+
+All VKs (`governance_virtual_key_provider_configs`) have:
+- `allow_all_keys=1` — set via SQL (Bifrost API PUT silently ignores this field)
+- `allowed_models` — explicit JSON model list as text in DB (SQL NULL = deny all with enforce_auth_on_inference=1)
+
+If models stop working after a Bifrost upgrade/restore, re-run `/tmp/fix_vk_final.py` on CT 104 and then:
+```bash
+sqlite3 /opt/stacks/ai/bifrost/data/config.db \
+  "UPDATE governance_virtual_key_provider_configs SET allow_all_keys=1;"
+docker compose -f /opt/stacks/ai/bifrost.yml up -d --force-recreate
+```
+
 ## Ops
 
 ```bash
@@ -111,8 +160,12 @@ curl -s http://localhost:14003/mcp \
 ### Add a new MCP client
 
 ```bash
+curl -sc /tmp/bfcookies http://localhost:14003/api/session/login \
+  -H "Content-Type: application/json" \
+  -d '{"username":"fkrebs","password":"tapirnase"}' > /dev/null
+
 curl -s -X POST http://localhost:14003/api/mcp/client \
-  -H "Authorization: Bearer sk-tapirnase" \
+  -b /tmp/bfcookies \
   -H "Content-Type: application/json" \
   -d '{
     "name": "<name>",