fix(mobile): polish channel management and iOS Settings (#8171)

## Summary

Use native iOS sheets for channel editing and Add Members, with profile
avatars, matching search, and destructive removal dialogs. Canvas
content becomes a tappable preview with Add/Remove actions.

Fix the Settings availability menu and clipped copy confirmation. Align
channel action messages with chat styling and keep agent identities
distinguishable across selection, attribution, and profile surfaces.

### Related issue

No duplicate found in the existing mobile Settings/channel issues and
PRs.

### Testing

- Flutter analysis, formatting, file-size checks, focused collision
regressions, and the full mobile test suite passed.
- Production UIKit picker simulator check passed: distinct
visible/accessibility labels, avatar updates, selected rows, and pubkey
callbacks. Wired into Mobile Swift CI.
- Original UI was built and tested on the physical iPhone with author
confirmation; profile/community data preserved.
- Review fixes await renewed author device confirmation before restoring
`buzz-review-completed` and ready-for-review status.

---------

Signed-off-by: kenny lopez <klopez4212@gmail.com>

.github/workflows/_ci-clients.yml

@@ -146,6 +146,7 @@ jobs:
           xcrun simctl boot "$device"
           xcrun simctl bootstatus "$device" -b
           /bin/bash scripts/test-mobile-pagination-accessibility.sh "$device"
+          /bin/bash scripts/test-mobile-member-picker.sh "$device"
       - name: Build complete unsigned iOS release
         run: |
           /bin/bash scripts/test-mobile-gateway-recipes.sh