Agent activity has a proper bridge into the app

Kaji now has a dedicated bridge for turning agent runs, provider activity, and notification context into app-level activity state. This makes the sidebar and navigation paths less dependent on scattered provider-specific assumptions.

• Added KajiAgentActivityBridge for mapping agent state into app activity
• Added KajiAgentActivityContextResolver and KajiAgentRunSummary
• Added AgentProviderCatalog as the central provider source
• Updated notification normalization and navigation for agent activity routes
• Added KajiAgentActivityBridgeTests and notification routing tests

Changed-file rows are easier to read and reuse

The VCS tab now separates changed-file presentation from the larger tab view. Rows understand their presentation mode directly, making file lists cleaner in regular VCS views and diff-focused contexts.

• Added VCSPresentationMode
• Extracted VCSChangedFileRow from VCSTabView
• Updated diff viewer tab creation and changed-file routing
• Added AppState diff viewer tests
• Bumped Kaji to 0.3.2