breakglass UI v2: attachable sessions (tmux model) + mobile-first redesign

Full audit-driven rework. Keeps the proven SSE-translation + verb logic; everything else upgraded for phone-primary use.

Backend — server owns the session, clients attach (Viktor's tmux idea):
- session.py: SessionManager + Session with an event log, subscriber pub/sub, and turns that run DETACHED (keep going if the client disconnects).
- GET /api/session/{id}/stream = attach (SSE): replays the transcript then tails live; per-event id: lines so an EventSource auto-reconnect resumes from Last-Event-ID (free re-attach). POST /{id}/prompt starts a detached turn; POST /{id}/cancel = Stop. Replaces the old one-shot /api/chat.
- agent_session trimmed to the argv + translate_event helpers; 21 new/updated tests (replay, Last-Event-ID resume, broadcast, detached turn, resume, cancel, routes) — 53 green.

Frontend — mobile-first via the frontend-design skill (emergency-console aesthetic):
- EventSource attach (native auto-reconnect, zero client reconnect logic); transcript.js folds events->messages with id-dedupe so replays never double-render (30 unit assertions).
- Installable PWA: manifest + icons (wrench/break-glass mark) + apple-mobile-web-app meta + theme-color; viewport-fit=cover + safe-area; 100dvh; 16px composer (no iOS zoom).
- One-tap diagnosis presets (Triage / Memory-OOM / Disk / Services / QEMU-wedged) mapped to the devvm's real failure modes; Stop button while a turn runs.
- Foldable VM-control sheet, cycle the dominant recovery action w/ confirm, output capped 46vh.
- a11y: fixed --ink-faint contrast 3.6:1 -> 6.1:1 (WCAG AA); >=44px tap targets. Deleted the obsolete fetch-reader sse.js (EventSource replaces it).

Verified: 53 backend tests + 30 transcript assertions; Playwright @390x844 (input on-screen y=721-821, presets/sheet/fold/cap); local integration smoke vs the real backend (attach->caught-up, 404, verbs, PWA served).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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