Add user location flow with map centering and temporary site creation

[wilhel1812]

Summary

Add a live user-position foundation that can center the map, show the current browser/device location, and let the user create an existing temporary Site draft from that position.

Desired behavior

• User starts the flow from a map control labeled Use my location.
• The browser/device location prompt is triggered by that explicit user action.
• While active, the app watches the user position and keeps a visible user-position marker and accuracy circle on the map.
• On the first successful location result after toggling on, the map centers on the returned location at zoom 12.
• The map continues following location updates until the user manually pans; after that, the marker keeps updating without recentering. Toggle off/on re-enables following.
• Clicking the user-position marker creates a temporary Site draft at the marker coordinates by reusing the existing temporary-site draft flow.
• Initial toggle-on does not automatically create a temporary Site draft.
• Saving the temporary Site uses the existing Save to Library flow and auto-inserts the saved Site into the current Simulation.
• Dismissing the temporary Site removes only the draft; the user-position marker remains visible while location is active.
• Turning location off stops live location, hides the marker/accuracy circle, and leaves any existing temporary Site draft alone.

Read-only behavior

• In read-only/shared contexts, the location marker and accuracy circle still work.
• Creating a temporary Site from the user-position marker is disabled in read-only contexts.

Out of scope

• Continuous simulation/PASS-list updates from live user position. That remains Phase 2 in Feature request: live simulation from user position (GPS/browser geolocation) #414.

Acceptance criteria

• The app can obtain user location from the browser/device after explicit user action.
• The map recenters on the first successful returned location at zoom 12.
• A live user-position marker and accuracy circle are shown while location is active.
• User-position updates move the marker while active.
• Manual map panning stops auto-follow without stopping marker updates.
• Clicking the user-position marker in editable mode reuses the existing temporary Site draft flow with the marker coordinates.
• Saving/dismising the temporary Site does not remove the user-position indicator while location is active.
• Read-only mode shows marker/accuracy but does not create a temporary Site.
• Location failures show plain app notifications; technical details are logged to console.

Related

• Feature request: live simulation from user position (GPS/browser geolocation) #414 is Phase 2 for continuous live simulation outputs and PASS-list updates.
• In site editor, when adding from map search, map should jump to the location when using the results. Currently, it does not jump to the location, and the user has to scroll to find the location on the map. #95 is related map-centering behavior but not a duplicate.

[heigre]

Clarification: treat this as Phase 1 (foundation) for user location UX.\n\nScope here is one-shot location flow: obtain location, recenter map, create temporary site, and keep a user-position indicator visible.\n\nRelated follow-up: #414 is Phase 2 (advanced) with continuous tracking + continuously updated live simulation/PASS list. #414 should build on this issue, not replace it.

[wilhel1812]

Implementation completed locally on branch issue/250-user-location-flow.

What changed:

• Added a Use my location map control using live browser geolocation tracking.
• Added user-position marker + accuracy circle while location is active.
• First successful location recenters the map at zoom 12; manual pan stops auto-follow while marker updates continue.
• Clicking the live user marker reuses the existing temporary Site draft path with the marker coordinates. No duplicate Site creation/save/library logic was added.
• Read-only mode shows marker/accuracy only and does not create a temporary Site.
• Location failures publish plain app notifications and log technical details to console.

Verification:

• npm test passed (427 tests).
• npm run build passed.
• No local deploy scripts were run.