feat: add 11 alert backends and fix PyPI/DEV.to search

Add Wikipedia, Stack Exchange, GitLab, npm, PyPI, Docker Hub,
arXiv, Lobsters, DEV.to, Medium, and Hugging Face backends to
the alert plugin (16 -> 27 total). Fix PyPI backend to use RSS
updates feed (web search now requires JS challenge). Fix DEV.to
to use public articles API (feed_content endpoint returns empty).

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

docs/CHEATSHEET.md

@@ -346,14 +346,16 @@ No API credentials needed (uses public GQL endpoint).
 !alert history <name> [n]        # Show recent results (default 5)
 ```
 
-Searches keywords across 16 backends: YouTube (yt), Twitch (tw), SearXNG (sx),
+Searches keywords across 27 backends: YouTube (yt), Twitch (tw), SearXNG (sx),
 Reddit (rd), Mastodon (ft), DuckDuckGo (dg), Google News (gn), Kick (kk),
 Dailymotion (dm), PeerTube (pt), Bluesky (bs), Lemmy (ly), Odysee (od),
-Archive.org (ia), Hacker News (hn), GitHub (gh). Names: lowercase alphanumeric +
-hyphens, 1-20 chars. Keywords: 1-100 chars. Max 20 alerts/channel. Polls every
-5min. Format: `[name/yt/a8k2m] Title -- URL`. Use `!alert info <id>` to see full
-details. No API credentials needed. Persists across restarts. History stored in
-`data/alert_history.db`.
+Archive.org (ia), Hacker News (hn), GitHub (gh), Wikipedia (wp),
+Stack Exchange (se), GitLab (gl), npm (nm), PyPI (pp), Docker Hub (dh),
+arXiv (ax), Lobsters (lb), DEV.to (dv), Medium (md), Hugging Face (hf).
+Names: lowercase alphanumeric + hyphens, 1-20 chars. Keywords: 1-100 chars.
+Max 20 alerts/channel. Polls every 5min. Format: `[name/yt/a8k2m] Title -- URL`.
+Use `!alert info <id>` to see full details. No API credentials needed. Persists
+across restarts. History stored in `data/alert_history.db`.
 
 ## SearX
 

docs/USAGE.md

@@ -660,10 +660,9 @@ Title Three -- https://example.com/page3
 
 ### `!alert` -- Keyword Alert Subscriptions
 
-Search keywords across multiple platforms (YouTube, Twitch, SearXNG, Reddit,
-Mastodon/Fediverse) and announce new results. Unlike `!rss`/`!yt`/`!twitch`
-which follow specific channels/feeds, `!alert` searches keywords across all
-supported platforms simultaneously.
+Search keywords across 27 platforms and announce new results. Unlike
+`!rss`/`!yt`/`!twitch` which follow specific channels/feeds, `!alert` searches
+keywords across all supported platforms simultaneously.
 
 ```
 !alert add <name> <keyword...>   Add keyword alert (admin)
@@ -699,6 +698,17 @@ Platforms searched:
 - **Archive.org** (`ia`) -- Internet Archive advanced search, sorted by date (no auth required)
 - **Hacker News** (`hn`) -- Algolia search API, sorted by date (no auth required)
 - **GitHub** (`gh`) -- Repository search API, sorted by recently updated (no auth required)
+- **Wikipedia** (`wp`) -- MediaWiki search API, English Wikipedia (no auth required)
+- **Stack Exchange** (`se`) -- Stack Overflow search API, sorted by activity (no auth required)
+- **GitLab** (`gl`) -- Public project search API, sorted by last activity (no auth required)
+- **npm** (`nm`) -- npm registry search API (no auth required)
+- **PyPI** (`pp`) -- Recent package updates RSS feed, keyword-filtered (no auth required)
+- **Docker Hub** (`dh`) -- Public repository search API (no auth required)
+- **arXiv** (`ax`) -- Atom search API for academic papers (no auth required)
+- **Lobsters** (`lb`) -- Community link aggregator search (no auth required)
+- **DEV.to** (`dv`) -- Forem articles API, tag-based search (no auth required)
+- **Medium** (`md`) -- Tag-based RSS feed (no auth required)
+- **Hugging Face** (`hf`) -- Model search API, sorted by downloads (no auth required)
 
 Polling and announcements:
 
@@ -706,7 +716,8 @@ Polling and announcements:
 - On `add`, existing results are recorded without announcing (prevents flood)
 - New results announced as `[name/<tag>/<id>] Title -- URL` where tag is one of:
   `yt`, `tw`, `sx`, `rd`, `ft`, `dg`, `gn`, `kk`, `dm`, `pt`, `bs`, `ly`, `od`, `ia`,
-  `hn`, `gh` and `<id>` is a short deterministic ID for use with `!alert info`
+  `hn`, `gh`, `wp`, `se`, `gl`, `nm`, `pp`, `dh`, `ax`, `lb`, `dv`, `md`, `hf`
+  and `<id>` is a short deterministic ID for use with `!alert info`
 - Titles are truncated to 80 characters
 - Each platform maintains its own seen list (capped at 200 per platform)
 - 5 consecutive errors doubles the poll interval (max 1 hour)