Add municipality and coordinate search, and a map target selector

Puts the controls that change what the map is looking at over the map itself,
where they act, and gives them something to search.

Search is one field, not two. A string either parses as coordinates or it does
not, and the answer is obvious from the text, so making the user declare up
front which kind of thing they are looking for would be asking them to do the
program's job. Coordinates accept decimal and degrees-minutes-seconds, comma or
space separated, with hemisphere letters — including the Italian O for ovest,
because someone reading an Italian map will type it and silently reading it as
east would put them the wrong side of Greenwich.

The 1180 Piedmont municipalities are bundled rather than geocoded online. The
app is region-scoped, so a list of one region's towns is small enough to ship
(100 KB) and beats a geocoder on every axis that matters: instant, offline, no
API key, no rate limit, and it cannot return a result somewhere the app has no
radar for. Matching folds accents, so "aglie" finds "Agliè", and prefix matches
outrank substring ones — typing "tor" should surface Torino, not the first
alphabetical name that happens to contain those letters.

tool/generate_places.py derives the list from Istat boundary shapefiles
(CC BY 4.0). Two properties of that file cost time and are now written down:
the geometry is UTM 32N rather than degrees, and the DBF is UTF-8 despite one
bilingual Friulian record that makes strict cp1252 fail. A terminal renders
utf-8 and latin-1 output identically, so the encoding cannot be settled by
looking at printed text — it took dumping codepoints. A guard in the generator
and a test against the shipped asset both check for mojibake now, and the guard
caught a real mistake the moment it was written.

The target selector switches between following the device, a saved place, and
the whole region, and the selection doubles as what the app reopens on: "the
place I marked" and "what I see when I open the app" are one idea to the person
using it. Dragging the map while it is following stops the camera chasing them
but leaves that preference alone, because looking somewhere else now is not the
same as changing their mind about next launch.

The position marker and the following are MapLibre's own, driven by
onCameraTrackingDismissed, so there is no second location stream to keep in step
with the map.

A test asserts that all 1180 municipalities fall inside the region bounds, which
is what actually validates the UTM-to-degrees conversion end to end.

Verified on the emulator: the dropdown lists follow, region and both saved
places; "aglie" finds Agliè; "44.3841 7.5426" offers the coordinate jump and
lands on Cuneo at town-reading zoom; selecting follow moves the map to the
device position with the blue dot on it and changes the recentre button to
match.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Nuvolari/app/lib/features/places/comuni_repository.dart

@@ -0,0 +1,37 @@
+import 'package:flutter/services.dart' show AssetBundle, rootBundle;
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../core/region/region_repository.dart';
+import 'comune.dart';
+
+/// Loads the bundled municipality list.
+class ComuniRepository {
+  const ComuniRepository({this.bundle});
+
+  /// Overridden in tests; null means the real asset bundle.
+  final AssetBundle? bundle;
+
+  AssetBundle get _assets => bundle ?? rootBundle;
+
+  static String assetPathFor(String regionId) =>
+      'assets/regions/${regionId}_comuni.json';
+
+  Future<ComuneIndex> load(String regionId) async {
+    final source = await _assets.loadString(assetPathFor(regionId));
+    return ComuneIndex.parse(source);
+  }
+}
+
+final comuniRepositoryProvider = Provider<ComuniRepository>(
+  (ref) => const ComuniRepository(),
+);
+
+/// The searchable municipality index for the active region.
+///
+/// Loaded once and kept: 1180 entries with a precomputed fold key is a
+/// negligible amount of memory next to a single radar frame, and rebuilding it
+/// per search would make typing feel slow for no reason.
+final comuneIndexProvider = FutureProvider<ComuneIndex>((ref) async {
+  final regionId = ref.watch(regionIdProvider);
+  return ref.watch(comuniRepositoryProvider).load(regionId);
+});