Add browser-tested frontend workflows

[R055LE]

What changed

• Fix point placement so the preview, coordinate fields, and saved outlet share one state.
• Let existing room walls be edited or removed individually.
• Confirm destructive point, room, panel, and circuit actions.
• Make point markers and circuit entries named, keyboard-operable controls.
• Stack the floorplan and details on phone-sized viewports.
• Add Playwright browser regressions to the frontend CI job with synthetic API fixtures.

Why

Agent-browser dogfooding reproduced two user-reported problems and found three related gaps. Outlet placement kept separate preview and form coordinates, so a later click moved the preview while save retained the first click. Room editing exposed the original append-and-undo builder, which made correcting an early wall require rebuilding later walls.

The browser pass also found immediate destructive actions, mouse-only floorplan controls, and an unusable compressed phone layout.

Impact

Frontend behavior now matches the state shown to the user. Browser regressions run against the real React application without requiring a deployed Hearth instance or household database.

Validation

• Frontend unit tests, lint, typecheck, and production build passed.
• Five Chromium browser regressions passed after failing against the original behavior.
• Backend lint and 23 tests passed.
• Rebuilt production container was healthy under the non-root, read-only runtime constraints.
• Final axe-core audit reported zero violations.
• Browser console and uncaught page errors were empty.
• Trivy's fixable HIGH/CRITICAL image gate reported zero findings.

Security posture

Playwright is a development dependency and is not copied into the distroless runtime. Browser fixtures contain synthetic data, so CI traces do not need real household records. Confirmation protects against operator mistakes; it is not an authorization control, and Hearth's private-network trust boundary remains unchanged.