feat(aisidebar): implement Ollama availability handling and graceful startup

- Add comprehensive Ollama connection error handling strategy
- Implement OllamaClient with non-blocking initialization and connection checks
- Create OllamaAvailabilityMonitor for periodic Ollama connection tracking
- Update design and requirements to support graceful Ollama unavailability
- Add new project structure for AI sidebar module with initial implementation
- Enhance error handling to prevent application crashes when Ollama is not running
- Prepare for future improvements in AI sidebar interaction and resilience

.kiro/specs/ai-sidebar-enhancements/tasks.md

@@ -97,7 +97,37 @@
   - Update message rendering to handle reasoning metadata
   - _Requirements: 5.5_
 
-- [ ] 8. Add error handling and edge cases
+- [-] 8. Implement graceful Ollama unavailability handling
+- [ ] 8.1 Update OllamaClient initialization
+  - Modify `__init__()` to never raise exceptions during initialization
+  - Add connection check that sets internal availability flag
+  - Update `list_models()` to return empty list instead of raising on connection failure
+  - Update `chat()` and `stream_chat()` to return error messages instead of raising
+  - _Requirements: 6.1, 6.3, 6.5_
+
+- [ ] 8.2 Create OllamaAvailabilityMonitor
+  - Create `ollama_monitor.py` with OllamaAvailabilityMonitor class
+  - Implement periodic availability checking using GLib.timeout_add (30s interval)
+  - Add callback mechanism to notify UI of state changes
+  - Ensure checks are non-blocking and don't impact UI responsiveness
+  - _Requirements: 6.4_
+
+- [ ] 8.3 Update SidebarWindow for Ollama unavailability
+  - Initialize OllamaAvailabilityMonitor in SidebarWindow
+  - Display "Ollama not running" status message when unavailable at startup
+  - Update model label to show connection status
+  - Disable input field when Ollama unavailable, show helpful message
+  - Add callback to re-enable features when Ollama becomes available
+  - _Requirements: 6.1, 6.2, 6.4_
+
+- [ ] 8.4 Add user-friendly error messages
+  - Display clear instructions when user tries to chat without Ollama
+  - Show notification when Ollama connection is restored
+  - Update all command handlers to check Ollama availability
+  - Provide actionable error messages (e.g., "Start Ollama with: ollama serve")
+  - _Requirements: 6.2, 6.3_
+
+- [ ] 9. Add error handling and edge cases
   - Implement stream timeout handling (60s limit) with cancellation
   - Add connection error recovery for streaming failures
   - Handle command execution during active streaming
@@ -105,10 +135,11 @@
   - Implement graceful degradation for missing preferences file
   - _Requirements: 1.4, 3.5, 4.3, 4.4_
 
-- [ ] 9. Polish and integration
+- [ ] 10. Polish and integration
   - Add CSS styling for system messages, reasoning content, and streaming indicator
   - Implement `/help` command to display available commands
   - Add visual feedback for command execution (loading states)
   - Ensure all UI updates maintain smooth scrolling behavior
   - Test keyboard focus management across all new widgets
-  - _Requirements: 1.3, 2.3, 3.5, 5.5_
+  - Add status indicator in UI showing Ollama connection state
+  - _Requirements: 1.3, 2.3, 3.5, 5.5, 6.2_