Route the Map Journal through useRegionInstall and share the download progress UI

[cursor]

Spec: Fowler-style refactoring review (cloud agent, 2026-08-05). Refactor only — no behavior change.

Blocked by: #148

What to change

components/map-journal.tsx (618 lines) reimplements machinery that already exists:

1. Region install FSM — MapJournal (~197–258, ~391–413) and components/region-tracer.tsx (~162–228) each inline the createRegionStore → installed/manifest/install flow that lib/offline-region/use-region-install.ts already provides (used only by OfflineMapsPage today). Extend the hook with the options they need (e.g. autoInstall, remote-preview) and route both through it.
2. Download progress UI ×2 — the trail-map-hero-progress block is duplicated between map-journal.tsx (~464–485) and components/offline-maps-page.tsx (~60–76). Extract a RegionDownloadProgress component.
3. Split the rest — extract useJournalMap (MapLibre mount, markers, GPS) and a JournalCaptureSheet component for the aside, leaving MapJournal as a shell. Use useOnline from the blocking ticket for the connectivity listener (~380–389).

Out of scope: map styling, offline pack format, RegionTracer's Playwright window hooks (keep the test seams).

Acceptance criteria

• MapJournal and RegionTracer consume useRegionInstall; no inline region-install FSM remains
• One RegionDownloadProgress component serves both surfaces
• mise run lint and mise run test pass (tests/outdoor-capture.spec.ts and offline-region specs unchanged)