feat: add inline project timeline and notes section to Project Detail

- Implemented a Gantt timeline using GanttChart component scoped to project checkpoints.
- Added functionality to create and manage checkpoints with AddCheckpointDialog.
- Introduced EditCheckpointDialog for editing existing checkpoints.
- Created a notes section displaying a list of notes with the ability to add new notes.
- Updated routing to include notes detail page.
- Enhanced GanttChart with context menu for editing and deleting checkpoints.
- Improved UI components for better user experience.

prd.json

@@ -278,8 +278,8 @@
         "Verify in browser using dev-browser skill"
       ],
       "priority": 15,
-      "passes": false,
-      "notes": ""
+      "passes": true,
+      "notes": "Completed: Project Timeline section using GanttChart (scoped to project checkpoints) with AddCheckpointDialog (defaultProjectId hides project selector), checkpoint delete mutation. Notes section using Item cards (variant=muted) in flex-wrap grid matching Figma design, '+ Add' creates note via notes.create and navigates to /notes/$noteId, clicking note card navigates to /notes/$noteId. Route stub at notes.$noteId.tsx with back button + note title."
     },
     {
       "id": "US-016",