feat: add comprehensive tagging system with cooccurrence tracking

- Add tags, project_tags, and tag_cooccurrence tables with proper indexes
- Implement full CRUD API endpoints for tag management
- Add tag association endpoints for projects with automatic cooccurrence updates
- Include related tags and project filtering by tag functionality

.sqlx/query-d449cad77fa2e65e2f4d1eec62daa09045e903648e615083500f0f373c4f3525.json

@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "DELETE FROM project_tags WHERE project_id = $1 AND tag_id = $2",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Uuid",
+        "Uuid"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "d449cad77fa2e65e2f4d1eec62daa09045e903648e615083500f0f373c4f3525"
+}