chore(workspace): add hardened startup/security workflows and skill suite

skills/calendar-sentinel/SKILL.md

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+---
+name: calendar-sentinel
+description: Monitor near-term calendar commitments, detect conflicts/risk windows, and produce concise actionable alerts. Use when users ask for schedule checks, next-24h scans, conflict detection, prep reminders, or proactive event watch behavior.
+---
+
+# Calendar Sentinel
+
+## Monitoring goals
+
+- Surface only schedule items that matter soon.
+- Detect conflicts and unrealistic transitions.
+- Provide practical prep reminders with lead time.
+
+## Default scan windows
+
+- Primary: next 24h
+- Priority alert: next 2h
+- Optional extension: next 48h when explicitly requested
+
+## Detection rules
+
+Flag events when any condition is true:
+
+1. Time overlap between two commitments.
+2. Back-to-back events with insufficient transition buffer.
+3. Missing critical event metadata (time/location/link) close to start.
+4. High-importance event starts soon and no prep reminder has been surfaced.
+
+## Alert policy
+
+- Keep alerts compact and actionable.
+- Batch related items into one update.
+- Avoid repeated alerts unless state changed or event entered a tighter window.
+
+## Output template
+
+Follow shared convention: `skills/_shared/briefing-conventions.md`
+
+- **Now (<2h):** immediate events and blockers
+- **Today (24h):** upcoming commitments and conflicts
+- **Risks:** overlap | travel buffer | missing details
+- **Next actions (1-3):** exact steps to de-risk schedule
+
+## Noise controls
+
+- If no conflicts/urgent events, return a brief all-clear.
+- Suppress duplicate reminders in short intervals.
+- Prefer one high-signal reminder over many low-signal pings.