feat(app,ui): add map-based location picker and geocoding

- introduce LocationPickerScreen with flutter_map for selecting and confirming
  locations, including markers and loading states
- integrate manual location editing in ReviewScreen and persist updated
  coordinates/address in the report
- add GeocodingService with Nominatim search, Photon fallback, reverse
  geocoding, debounced queries, caching, and timeouts
- update i18n (en) with new map/location strings; remove unused onboarding
  and welcome texts

assets/lang/en.json

@@ -33,6 +33,10 @@
   "btn.ok": "OK",
   "btn.yes": "Yes",
   "btn.no": "No",
+  "btn.editLocation": "Edit Location",
+  "btn.searchLocation": "Search Location",
+  "btn.useThisLocation": "Use This Location",
+  "btn.currentLocation": "Use Current Location",
   "label.category": "Category",
   "label.severity": "Severity",
   "label.status": "Status",
@@ -81,20 +85,6 @@
   "settings.theme.dark": "Dark",
   "lang.en": "English",
   "lang.ms": "Bahasa Malaysia",
-  "welcome.title": "Snap. Detect. Fix.",
-  "welcome.subtitle": "Report city issues in seconds with AI-powered detection. Help create safer, better communities together.",
-  "cta.continueGuest": "Continue as guest",
-  "cta.signIn": "Sign in",
-  "cta.skip": "Skip",
-  "cta.next": "Next",
-  "cta.getStarted": "Get started",
-  "onboarding.header": "Welcome to CityPulse",
-  "onboarding.title1": "Fast Issue Reporting",
-  "onboarding.body1": "Simply take a photo of any urban issue - our AI automatically identifies and categorizes the problem in seconds.",
-  "onboarding.title2": "Smart City Mapping",
-  "onboarding.body2": "View all reported issues on an interactive map with intelligent clustering and filtering options.",
-  "onboarding.title3": "Track Progress",
-  "onboarding.body3": "Follow the status of your reports from submission to resolution. Help make your community better.",
   "auth.title": "Sign in",
   "auth.signInWithApple": "Sign in with Apple",
   "auth.signInWithGoogle": "Sign in with Google",
@@ -153,5 +143,16 @@
   "confirm.logout.title": "Logout?",
   "confirm.logout.message": "You will be returned to the welcome screen.",
   "label.createdAt": "Created At",
-  "error.clearData": "Failed to clear data"
+  "error.clearData": "Failed to clear data",
+  "map.searchHint": "Search for a location...",
+  "map.selectLocation": "Select Location",
+  "map.selectedLocation": "Selected Location",
+  "map.confirmLocation": "Confirm this location?",
+  "map.currentLocation": "Current Location",
+  "map.searching": "Searching...",
+  "map.noResults": "No results found",
+  "map.moveMapToSelect": "Move the map to select a location",
+  "map.loadingMap": "Loading map...",
+  "map.gettingAddress": "Getting address...",
+  "map.continueAnyway": "Continue Anyway"
 }