[JaeTierce31]

Purpose

Verify the first MappedFair offline venue and itinerary slice at the browser boundary before merging foundation PR #2 into main. This stacks on feat/mappedfair-foundation and is tracked by J3S-35.

Changes

• Add Chromium acceptance test against the built Vite preview: initial online load and service worker activation, ordered stops/notes saved to IndexedDB, offline reload, an offline edit, and recovery after reconnect.
• Check that denied IndexedDB access reports an error and never claims a successful save; check narrow-viewport horizontal overflow.
• Install Chromium in CI after build and run the two browser tests. Document the local command.

Evidence

• Local lint, 2 Vitest tests, typecheck, build, and playwright test --list passed.
• Local browser execution is unverified here: this workspace lacks the Chromium executable. The new CI job installs it and is the authoritative browser run for this PR.
• A passing Chromium test covers the tested viewport and browser only; human mobile usability and ADR-001 source-rights ratification remain gates on PR chore: establish MappedFair app foundation #2.

Review focus

Check that the test truly performs an offline navigation from the precached shell and verifies user data after a reload; check storage-denied behavior and any CI browser failure before merging.