feat(auth): add /api/me endpoint, avatar upload, and profile picture support

- Add migration 005: nullable avatar_url column on users table
- Add GET /api/me: returns id, username, avatar_url from DB (fixes UUID-on-profile bug)
- Add PUT /api/me/avatar: accepts raw image bytes (≤1 MB, jpeg/png/webp/gif),
  writes to avatars/ dir, updates avatar_url in DB
- Serve /avatars via ServeDir so uploaded images are publicly accessible
- Update account.html: fetch username from /api/me instead of parsing JWT;
  add circular avatar display with initials fallback and click-to-upload
- Add SolitaireServerClient::fetch_me() for desktop/Android profile display
- Add avatar_url field to SyncBackend::SolitaireServer settings (serde default None)
- Update sqlx offline query cache for new avatar_url queries

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.sqlx/query-06c945e50567c6801f1346d436cdc86a82a4e13dd45d8286295ba37cdbdc045e.json

@@ -0,0 +1,20 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT username FROM users WHERE id = ?",
+  "describe": {
+    "columns": [
+      {
+        "name": "username",
+        "ordinal": 0,
+        "type_info": "Text"
+      }
+    ],
+    "parameters": {
+      "Right": 1
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "06c945e50567c6801f1346d436cdc86a82a4e13dd45d8286295ba37cdbdc045e"
+}

.sqlx/query-15d08e02b102147bc74848ec3692b99edbf4c33078191f0132991ee94d4507b1.json

@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "UPDATE users SET avatar_url = ? WHERE id = ?",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 2
+    },
+    "nullable": []
+  },
+  "hash": "15d08e02b102147bc74848ec3692b99edbf4c33078191f0132991ee94d4507b1"
+}

.sqlx/query-f23630e78ae88e72d7930184f7cd8fc67e71f3930609f1cf14061d35d6de8ec3.json

@@ -1,12 +0,0 @@
-{
-  "db_name": "SQLite",
-  "query": "INSERT OR IGNORE INTO analytics_events\n               (id, user_id, session_id, event_type, payload, client_time, received_at)\n               VALUES (?, ?, ?, ?, ?, ?, ?)",
-  "describe": {
-    "columns": [],
-    "parameters": {
-      "Right": 7
-    },
-    "nullable": []
-  },
-  "hash": "f23630e78ae88e72d7930184f7cd8fc67e71f3930609f1cf14061d35d6de8ec3"
-}

.sqlx/query-fae33e7159b43c756131b1545360dcb0250988b43550881e3f0a336d9516dd45.json

@@ -0,0 +1,26 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT username, avatar_url FROM users WHERE id = ?",
+  "describe": {
+    "columns": [
+      {
+        "name": "username",
+        "ordinal": 0,
+        "type_info": "Text"
+      },
+      {
+        "name": "avatar_url",
+        "ordinal": 1,
+        "type_info": "Text"
+      }
+    ],
+    "parameters": {
+      "Right": 1
+    },
+    "nullable": [
+      false,
+      true
+    ]
+  },
+  "hash": "fae33e7159b43c756131b1545360dcb0250988b43550881e3f0a336d9516dd45"
+}