chore(docs): retire dead fable-mcp wheel-distribution refs; untrack docs/superpowers

The old standalone fable-mcp wheel/download flow is gone from code (no route,
no Dockerfile build, no FABLE_MCP_DIST_DIR). Update api-keys-and-mcp,
api-reference, architecture, configuration, development to describe the
in-app HTTP MCP at /mcp (Bearer auth). Untrack the 18 committed
docs/superpowers/ files so the existing .gitignore takes effect.

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

docs/api-reference.md

@@ -179,12 +179,11 @@ All endpoints require login (session cookie or `Authorization: Bearer <api-key>`
 | POST | `/api/api-keys` | Create key `{name, scope}` → `{key, ...}` (key shown once) |
 | DELETE | `/api/api-keys/:id` | Revoke key |
 
-## Fable MCP Distribution
+## Scribe MCP
 
-| Method | Path | Description |
-|--------|------|-------------|
-| GET | `/api/fable-mcp/info` | `{available: bool, filename: string\|null}` |
-| GET | `/api/fable-mcp/download` | Download wheel file |
+The MCP tool surface is served at `POST /mcp` (streamable HTTP, Bearer auth) by
+the in-app server in `src/scribe/mcp/`. It is not a REST surface — see
+[API Keys and Scribe MCP](api-keys-and-mcp.md) for client configuration.
 
 ## Notifications