Add database optimizations for photo search and pagination

Implement database-level sorting with composite indexes for efficient date and tag queries. Add pagination metadata support and optimize tag count queries using batch processing.

src/data/mod.rs

@@ -101,6 +101,16 @@ impl FromRequest for Claims {
 pub struct PhotosResponse {
     pub photos: Vec<String>,
     pub dirs: Vec<String>,
+
+    // Pagination metadata (only present when limit is set)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub total_count: Option<i64>,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub has_more: Option<bool>,
+
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub next_offset: Option<i64>,
 }
 
 #[derive(Copy, Clone, Deserialize, PartialEq, Debug)]
@@ -141,6 +151,10 @@ pub struct FilesRequest {
 
     // Media type filtering
     pub media_type: Option<MediaType>,
+
+    // Pagination parameters (optional - backward compatible)
+    pub limit: Option<i64>,
+    pub offset: Option<i64>,
 }
 
 #[derive(Copy, Clone, Deserialize, PartialEq, Debug)]