feat(wiki): docs-lookup plugin against Quartz contentIndex

New maubot plugin that points at any Quartz-rendered docs site and
answers chat queries by full-text searching its emitted
/static/contentIndex.json. Default config targets docs.ariege.io
(castle-docs).

Commands:
  !ask <query>            search corpus; top-N hits with snippet + link
  !doc <slug-or-title>    open a specific page (fuzzy title match)
  !wiki / !wiki refresh   status / force re-index

Architecture:
- Periodic fetch (default 10 min) of /static/contentIndex.json
- In-memory inverted-ish scoring: title hit 5pt, content hit 1pt + freq
- No LLM — pure deterministic keyword search; RAG is future Phase 2b
- No DB — index is upstream-derived cache, repopulates on bot restart

Deployment posture: docs.ariege.io is served from cfaun alongside
maubot, so the bot hits it over the host's internal network — works
during WAN outages. base-config.yaml exposes docs_url + index_path
for adopters pointing at their own site.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -11,6 +11,7 @@ castle hosts; the actual plugin code lives here.
 |---|---|
 | [`journal/`](./journal/) | Farm-journal bot. `!journal <text>` records what you did, scoped per-user/room/timestamp. `!journal show [@user]` and `!journal today` query back. |
 | [`tracker/`](./tracker/) | Community-organizer bot. `!add` / `!task` / `!sidequest` / `!remind` / `!done` / `!list` / `!setup`. Implements the [Community Organizer spec](./docs/community-organizer-spec.md) — per-room shortcuts, 5-level priority, rules-based inbox classifier. |
+| [`wiki/`](./wiki/) | Docs-lookup bot. `!ask <query>` / `!doc <slug-or-title>` / `!wiki [refresh\|status]`. Points at any Quartz-rendered docs site (default: `docs.ariege.io`), full-text searches the corpus, replies with snippets + links. Internal-network deployment posture — works during WAN outages. |
 
 ## Community Organizer protocol