- Show all saved locations immediately when clicking "Change location"
- Add cancel button (X) to restore previous selection
- Click-away also restores previous selection (safe default)
- Hide "Add new address" link when a location is already selected

…bypass

The geocode_if_changed function was checking changeset.attributes
for existing coordinates, which includes ALL attributes (defaults,
prior values) not just explicitly provided ones. This caused flaky
test failures when concurrent tests set latitude/longitude.

Now checks for :provided_latitude/:provided_longitude arguments,
which are the explicit signal from ApplyProvidedCoordinates.

… flaky tests

Root cause: provided_latitude/provided_longitude were public arguments
on the huddl create/update actions. Ash.Generator auto-generates random
float values for public arguments, so concurrent tests randomly populated
these coordinates, causing ApplyProvidedCoordinates to bypass geocoding
unexpectedly.

- Mark provided_latitude/longitude as public?: false on both actions
- Use before_submit + force_set_argument to pass coordinates from
  the LiveView form (private args can't be set via form params)
- Add deterministic unit test for geocode_if_changed that catches the
  bug: constructs a changeset with pre-existing lat/lng attributes and
  verifies geocoding still runs when provided_* arguments are absent
- Update existing tests to set private arguments before for_create

- Replace inline LocationAutocomplete with route-based modal pattern
  on both group create and edit forms
- Modal filters to city/region types (locality, sublocality,
  administrative_area_level_2) for consistent UX
- Add ApplyProvidedCoordinates change to bypass geocoding when
  coordinates are provided from the frontend
- Add provided_latitude/longitude arguments to create_group and
  update_details actions
- Use force_change_attribute in before_submit to set coordinates
  directly (before_submit runs after action changes)
- Add tests verifying city picker UI, modal content, and
  clear/set/save flow on the edit page

…helpers

- Extract ApplyProvidedCoordinates to shared Huddlz.Geocoding module,
  removing duplicate Group and Huddl versions
- Move load_group_locations/2 to FormHelpers, removing duplicates from
  Edit, New, and Locations LiveViews
- Add missing @impl true annotations on handle_event/handle_info callbacks
- Extract reset_modal_state/1 helper in Locations LiveView
- Skip redundant group reload in Locations handle_params when slug unchanged

…licate group helpers

- Fix prepare_source_with_coordinates to use force_change_attribute
  instead of force_set_argument, since before_submit runs after
  for_create (Ash changes have already executed by that point)
- Extract inject_group_location_param and apply_group_location_to_form
  to FormHelpers, removing duplicates from GroupLive.New and Edit