release: v1.2.0 — unified images/ storage and legacy migration

Consolidate local images under data/images/, add docker migrate CLI,
startup index sync with orphan cleanup, and remove upload folder UI/API.

server/utils/content-type.ts

@@ -0,0 +1,20 @@
+export function contentTypeFromKey(key: string): string {
+  const ext = key.split('.').pop()?.toLowerCase()
+  switch (ext) {
+    case 'jpg':
+    case 'jpeg':
+      return 'image/jpeg'
+    case 'png':
+      return 'image/png'
+    case 'gif':
+      return 'image/gif'
+    case 'webp':
+      return 'image/webp'
+    case 'svg':
+      return 'image/svg+xml'
+    case 'ico':
+      return 'image/x-icon'
+    default:
+      return 'application/octet-stream'
+  }
+}