Map tiles: move to config + attribution (keep Google)

[adedw]

What to build

The Google tile URL is hardcoded and duplicated in the Index and Add map page scripts; Google tile usage outside the official Maps JS API is a ToS gray zone. Decision (made during ticketing): keep Google tiles — move the URL to configuration as a single source consumed by both pages, and add a proper attribution layer on the map.

Acceptance criteria

• No hardcoded tile URL in page scripts; both Index and Add read it from configuration (e.g. settings → serialized config endpoint or data attribute).
• Map displays tile attribution.
• Switching tile host afterwards requires only a config change.

Blocked by

None (can start immediately).