feat: saved custom places + home location (signed-in, private)

[AnayDhawan]

Signed-in users can save their own places privately to their account. Private to the user only; the public dataset is unchanged.

Scope

• Saved custom places: a logged-in user can add/edit/delete their own places (name, type, lat/lng, address, note). These render as a private pin layer merged client-side on top of the public getPlaces() set; only the owner sees them.
• Home location: user can save a home location (lat/lng, label). The existing "Nearest to you" / distance sort (placesByDistance in src/lib/geo.ts) can then sort against saved home, not just live geolocation.
• Search over saved places: a search box scoped to the user's saved places (name match), separate from the public filter-panel search.
• City filter over saved places: filter the user's saved places by their saved cities.

Backend (Supabase + RLS)

• user_places (user_id, name, type, lat, lng, address, note, created_at)
• user_home (user_id, lat, lng, label)
• Row-Level Security: each row readable/writable only by its owner (auth.uid() = user_id).

Behaviour

• Hydrate saved data on login; feature hidden when logged out.
• Degrade cleanly: no saved data => no private layer, public map unaffected.

Acceptance

• A logged-in user saves a place + a home location; both persist across reload.
• Saved places are searchable and filterable by city.
• Nearest-to-home ordering works off the saved home.
• A different account cannot see another user's saved places or home.