Android: add a 'take snapshot' button to the Live top bar (picture-with-+ icon)

[badbread]

The Android Live view has no snapshot control. Snapshot capture already exists elsewhere in the app (Playback/Clips save a frame — see ClipsScreen.kt "Snapshot saved to $path", saved to the device gallery via MediaStore per CacheJanitor). Live should have the same.

Ask

• Add a take-snapshot button to the Live screen's top-bar icon row (next to the grid/fullscreen icons — coordinate with Android: declutter Live top bar — move grid/fullscreen icons to the view-chips row; make both bars horizontally scrollable #161 which relocates those to the view-chips row). Icon: a picture with a + (e.g. Icons.AddPhotoAlternate / add_a_photo).
• Capture the current live frame. Decide the sensible target: the maximized/focused camera when one is open, else the wall (or per-tile). Mirror the desktop client's Live snapshot behavior where practical.
• Reuse the existing snapshot save path (MediaStore → gallery) so it lands with the Playback/Clips snapshots.
• Pair with the save toast + share action in the sibling issue (share sheet).

Queued after #156 / #162 / #160 / #161.

[badbread]

Implemented in #166 (Live take-snapshot button on the second bar; server full-res frame saved to gallery).