#178 feat(#161): release update notification in fleet_status

[Anonymous]

Originally created by: kumaakh

Summary

• #161 feat(T3.2): Release update notification — new src/services/update-check.ts fires a fire-and-forget GitHub releases fetch on server start (5s timeout, silent on failure); caches result; fleet_status prepends a one-line notice when a newer stable release is available; JSON format adds updateAvailable object; pre-release tags (alpha/beta/rc) are ignored; SKILL.md updated to instruct PM to surface the notice; adds 10 unit tests

Note: cleanupStaleTasks() wiring (T2.2) is intentionally omitted here — it ships in its own PR (#175).

Test plan

• [ ] CI green (813 tests passing locally)
• [ ] fleet_status shows an update notice when a newer stable release exists on GitHub
• [ ] No notice shown for pre-release tags or when already on latest
• [ ] Server start is not delayed by the update check (fire-and-forget)

🤖 Generated with Claude Code

[Anonymous]

Ticket changed by: kumaakh

• status: open --> closed