feat(room): collapse adjacent small state events with smart summaries

[tyreseluo]

Summary

• implement collapsible groups for adjacent small state events in the timeline (issue fix: clear Makepad DSL runtime errors and test-code clippy warnings #118)
• add expand/collapse toggle behavior with collapsed-by-default groups
• render collapsed summary as a smarter sentence-style description (join/leave/profile picture/display name/other state changes)
• refine toggle visual style to match lightweight timeline UI affordances
• place expanded-state collapse control on its own header row

Details

• timeline grouping and expanded-state tracking are handled in TimelineUiState
• collapsed groups render a dedicated summary row and hide interior small state rows
• expanded groups render all items while showing only a right-aligned collapse control
• i18n strings were updated for new small-state group actions and text

Validation

• cargo build --locked passes

Notes

• includes the lockfile package-version sync for robrix