Add location search, home/fit map buttons, and slim OSM attribution

- TopNavBar: Nominatim geocoding search field plus Home (center on first
  waypoint) and Fit (zoom to mission bounds) buttons (HTML prototype:
  #searchWrap/#homeBtn/#fitBtn). Both show a SnackBar instead of doing
  nothing when there are no waypoints yet.
- Renders as its own bar just below TopModeBar rather than fused into the
  same pill: TopModeBar lives in AppShell, a layer above PlanScreen, which
  owns the MapController these actions actually need. Fusing them would
  need lifting the MapController to shared state - reasonable follow-up
  if pixel-fidelity with the prototype's single bar matters later, but
  not necessary for the functionality itself.
- Replaced SimpleAttributionWidget with a compact custom attribution: OSM's
  tile usage policy requires visible attribution to stay, so instead of
  removing it (as first asked) I shrank it and dropped the "flutter_map |"
  prefix per the user's follow-up choice, so it reads cleanly against the
  now-opaque bottom bar instead of looking like a second banner.

Added 5 tests (nav bar renders, home/fit SnackBars with no waypoints,
empty search is a no-op). All 26 tests and flutter analyze pass. Verified
on the Pixel_10a emulator: searched "Berlin" and confirmed the map flew
there, dropped a waypoint, panned far away, and confirmed Home re-centers
and snaps onto it exactly.

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

app/lib/ui/screens/plan/plan_screen.dart

@@ -1,9 +1,11 @@
 import 'dart:async';
+import 'dart:convert';
 import 'dart:math' as math;
 
 import 'package:flutter/material.dart';
 import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:http/http.dart' as http;
 import 'package:latlong2/latlong.dart';
 
 import '../../../domain/mission/default_drone_profile.dart';
@@ -15,6 +17,7 @@ import '../../widgets/halo_menu.dart';
 import '../../widgets/mini_altitude_profile.dart';
 import '../../widgets/mission_map.dart';
 import '../../widgets/reticle_button.dart';
+import '../../widgets/top_nav_bar.dart';
 import '../../widgets/value_wheel.dart';
 import '../../widgets/waypoint_list_panel.dart';
 
@@ -254,6 +257,68 @@ class _PlanScreenState extends ConsumerState<PlanScreen> {
     _handleMoveEnd();
   }
 
+  /// Ortssuche per Nominatim-Geocoding (HTML-Demonstrator: doSearch()).
+  /// Zentriert die Karte auf den ersten Treffer.
+  Future<void> _onSearch(String query) async {
+    final q = query.trim();
+    if (q.isEmpty) return;
+    final messenger = ScaffoldMessenger.of(context);
+    try {
+      final uri = Uri.https('nominatim.openstreetmap.org', '/search', {
+        'format': 'json',
+        'addressdetails': '1',
+        'accept-language': 'en',
+        'limit': '1',
+        'q': q,
+      });
+      final response = await http
+          .get(uri, headers: {'User-Agent': 'dmc_app (Drone Mission Control)'});
+      final results = jsonDecode(response.body) as List;
+      if (results.isEmpty) {
+        messenger.showSnackBar(const SnackBar(content: Text('Location not found')));
+        return;
+      }
+      final first = results.first as Map<String, dynamic>;
+      final lat = double.parse(first['lat'] as String);
+      final lon = double.parse(first['lon'] as String);
+      _mapController.move(LatLng(lat, lon), 15);
+      _handleMoveEnd();
+    } catch (_) {
+      messenger.showSnackBar(const SnackBar(content: Text('Search failed')));
+    }
+  }
+
+  /// Zentriert auf den ersten Wegpunkt (HTML-Demonstrator: homeBtn).
+  void _onHomePressed() {
+    final waypoints = ref.read(currentMissionProvider);
+    if (waypoints.isEmpty) {
+      ScaffoldMessenger.of(context)
+          .showSnackBar(const SnackBar(content: Text('No waypoints yet')));
+      return;
+    }
+    final home = waypoints.first;
+    _mapController.move(LatLng(home.lat, home.lon), 16);
+    _handleMoveEnd();
+  }
+
+  /// Zoomt auf die gesamte Mission (HTML-Demonstrator: fitToWaypoints()).
+  void _onFitPressed() {
+    final waypoints = ref.read(currentMissionProvider);
+    if (waypoints.isEmpty) {
+      ScaffoldMessenger.of(context)
+          .showSnackBar(const SnackBar(content: Text('No waypoints to fit')));
+      return;
+    }
+    final points = [for (final w in waypoints) LatLng(w.lat, w.lon)];
+    _mapController.fitCamera(
+      CameraFit.bounds(
+        bounds: LatLngBounds.fromPoints(points),
+        padding: const EdgeInsets.fromLTRB(50, 50, 50, 140),
+      ),
+    );
+    _handleMoveEnd();
+  }
+
   /// Oeffnet die Wegpunktliste als eigene Vollbild-Route statt als
   /// internen Stack-Overlay, damit sie wirklich alles ueberdeckt -
   /// inklusive der Kopfleiste im AppShell darueber.
@@ -357,6 +422,21 @@ class _PlanScreenState extends ConsumerState<PlanScreen> {
               ),
           ],
         ),
+        Positioned(
+          // Direkt unterhalb der Plan/Fly-Kopfleiste (AppShell/TopModeBar),
+          // dieselbe Hoehe wie der Start der Draeder (top:56) - dort ist
+          // die Kopfleiste garantiert bereits zu Ende.
+          top: 62,
+          left: 0,
+          right: 0,
+          child: Center(
+            child: TopNavBar(
+              onSearch: _onSearch,
+              onHome: _onHomePressed,
+              onFit: _onFitPressed,
+            ),
+          ),
+        ),
         if (_mode == _ReticleMode.editing && targetWaypoint != null)
           Align(
             alignment: Alignment.center,