[codex] Simplify alert spec

[nedtwigg]

Summary

• Rewrites docs/specs/alert.md as a shorter behavioral reference.
• Keeps the public alert state contract, protocol anchors, command-exit rules, UI contract, security notes, and verification checklist.
• Reduces the spec from 904 lines to 338 lines by removing duplicated narrative, repeated transition prose, and long scenario walkthroughs.

Impact

This is documentation-only. The alert implementation and public behavior are unchanged.

Validation

• git diff --check -- docs/specs/alert.md
• pnpm --filter dormouse-lib test -- src/lib/alert-manager.test.ts src/lib/activity-monitor.test.ts src/lib/terminal-protocol.test.ts src/lib/terminal-registry.alert.test.ts

[cloudflare-workers-and-pages]

Deploying mouseterm with    Cloudflare Pages

Latest commit:	a39d13f
Status:	✅  Deploy successful!
Preview URL:	https://1e7b449f.mouseterm.pages.dev
Branch Preview URL:	https://simplify-alert-spec.mouseterm.pages.dev

View logs