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/configuration.md

@@ -58,12 +58,6 @@ See [sso-oauth.md](sso-oauth.md) for provider-specific setup.
 | `LOG_RETENTION_DAYS` | `90` | Days to keep app logs before automatic pruning |
 | `DATA_DIR` | `/data` | Root directory for persistent data (VAPID keys, backups) |
 
-### Fable MCP Distribution
-
-| Variable | Default | Description |
-|----------|---------|-------------|
-| `FABLE_MCP_DIST_DIR` | `/app/dist` | Directory where the bundled `fable-mcp` wheel is placed at build time |
-
 ## Docker Compose Setup
 
 ### Development (`docker-compose.yml`)