Refactor calendar datasource architecture

Centralizes date calculation logic into DateColumnDataSource
Improves separation of concerns across rendering components

Key changes:
- Introduces IColumnInfo interface for flexible column data
- Moves date calculation from multiple managers to dedicated datasource
- Removes duplicate date rendering logic
- Prepares architecture for future resource-based views

.claude/settings.local.json

@@ -0,0 +1,9 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(npm run build:*)"
+    ],
+    "deny": [],
+    "ask": []
+  }
+}