## Summary
- Make channel join/leave activity use the selected inline avatar-stack
treatment.
- Group related membership activity for one hour and preserve
profile/overflow-name interactions.
- Restore the virtualized day-divider handoff and align the sticky date
behavior with the message timeline.
## Validation
- `pnpm check`
- `pnpm test`
- `cargo test --manifest-path desktop/src-tauri/Cargo.toml`
- Visual desktop screenshot captured with seeded membership activity
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Signed-off-by: kenny lopez <klopez4212@gmail.com>
