Replace the default Flutter icon with a stylised cloud

The app shipped the Flutter template's blue F, which said nothing about what it
does and did not match the interface. The launcher icon is now a white cloud on
the same seed blue the app themes itself with, so the two read as one product.

The icon is drawn rather than hand-edited: tool/generate_icon.py renders it from
signed distance fields — a union of three circles and a rounded box — using only
the standard library, so regenerating it needs no image toolchain. The shape's
framing is derived from its own bounding box, which is what keeps it centred;
maintaining the bounds separately from the shape had it drifting off-centre.

Adds the adaptive icon and the Android 13 monochrome layer, which were missing
entirely. The generator frames the cloud against the 72dp the launcher mask
always keeps and adaptive_icon_foreground_inset is 0, so the layer is not shrunk
twice and the icon reads at the same size as its neighbours on a home screen.

Verified on the emulator: the cloud appears in the app drawer and holds its shape
down to 48px. docs/architecture.md records how to regenerate it, including the
flutter_launcher_icons 0.14.4 bug that writes a string into a boolean Xcode
setting and needs reverting by hand afterwards.

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

Nuvolari/CLAUDE.md

@@ -77,6 +77,9 @@ grounds that there are no ads today.
   generated by tool/generate_places.py. Offline search, no geocoding service. The source
   DBF is UTF-8 despite appearances and the geometry is UTM 32N — see docs/data-sources.md
   before regenerating.
+- Launcher icon: a white cloud on the seed blue #1F6FB2, drawn by tool/generate_icon.py
+  and expanded by flutter_launcher_icons. Read the "Launcher icon" section of
+  docs/architecture.md before regenerating: the tool corrupts an Xcode build setting.
 
 ## Verification loop (run after each milestone)
 - `dart format .` ; `flutter analyze` ; `flutter test` ; `flutter build appbundle`