Improve Von mobile PWA icons and Android masking

[witbrock]

Change

Simplify Von’s robot/flask mark for mobile launcher readability, retaining the smiling robot and replacing small flask details with one larger bubble. Update the standard 192/512px icons, add a separately padded 512px Android maskable icon and a dedicated 180px Apple touch icon, and version the manifest/Apple asset URLs.

Native task: #V#task_agent_44b3548893ec4094ed5500023650b9d1.

Validation

• pdm run pytest tests/backend/test_web_push.py -q: 29 passed.
• Flask test-client reads: manifest and all three referenced icons return 200; decoded sizes match the manifest; Apple template points to the 180px asset.
• Every light foreground pixel in the maskable asset lies within radius 181.51px (safe radius 204.8px).
• Chromium preview inspected at 32/48/96px, including circular and rounded-square masks; evidence retained in .run/pwa-icon/preview.png in the task worktree.
• git diff --check passed.

Assets were edited using the built-in image-generation tool from the existing icon, then cropped/resampled for platform sizes. Physical-device installation and existing-home-screen icon refresh were not tested; existing installations may require re-adding the shortcut. Public DGX deployment is requested via the coding controller after merge.