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-df4b8594ebbe7c0cfdfaa03a954931d50e87bb52bc4131c0b4803a57688d19ff.json

@@ -0,0 +1,38 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n        SELECT id, slug, name, created_at\n        FROM tags\n        ORDER BY name ASC\n        ",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "id",
+        "type_info": "Uuid"
+      },
+      {
+        "ordinal": 1,
+        "name": "slug",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 2,
+        "name": "name",
+        "type_info": "Text"
+      },
+      {
+        "ordinal": 3,
+        "name": "created_at",
+        "type_info": "Timestamptz"
+      }
+    ],
+    "parameters": {
+      "Left": []
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      false
+    ]
+  },
+  "hash": "df4b8594ebbe7c0cfdfaa03a954931d50e87bb52bc4131c0b4803a57688d19ff"
+}