docs: update docs for cron, shortener, CI

Add !cron section to USAGE.md and CHEATSHEET.md.
Mark cron, URL shortener, CI complete in ROADMAP.md and TODO.md.
New sprint in TASKS.md.

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

ROADMAP.md

@@ -113,7 +113,7 @@
 - [ ] Multi-server support (per-server config, shared plugins)
 - [ ] Stable plugin API (versioned, breaking change policy)
 - [x] Paste overflow (auto-paste long output to FlaskPaste, return link)
-- [ ] URL shortener integration (shorten URLs in alerts and long output)
+- [x] URL shortener integration (shorten URLs in subscription announcements)
 - [ ] Webhook listener (HTTP endpoint for push events to channels)
 - [ ] Granular ACLs (per-command permission tiers: trusted, operator, admin)
 - [x] `paste` command (manual paste to FlaskPaste)
@@ -125,6 +125,6 @@
 - [x] `jwt` plugin (decode tokens, show claims/expiry, flag weaknesses)
 - [x] `mac` plugin (OUI vendor lookup, local IEEE database)
 - [x] `pastemoni` plugin (monitor paste sites for keywords)
-- [ ] `cron` plugin (scheduled bot commands on a timer)
+- [x] `cron` plugin (scheduled bot commands on a timer)
 - [x] Plugin command unit tests (encode, hash, dns, cidr, defang)
-- [ ] CI pipeline
+- [x] CI pipeline (Gitea Actions, Python 3.11-3.13, ruff + pytest)