feat: frontend-ready backend — pagination, auto-derivatives, list endpoints, bulk ops, OpenAPI

Pagination: count_by_owner + count_search on AssetRepository,
timeline/search return real total count (not page len).

Auto-derivatives: worker enqueues GenerateDerivative when
ExtractMetadata job completes, closing the upload→thumbnail gap.

List endpoints: GET /albums, GET /stacks with user scoping.
ListAlbumsHandler, ListStacksHandler, find_by_owner on AssetStackRepository.

Tag filtering: tag_name field on AssetFilters, JOIN asset_tags+tags
in postgres search/count queries.

Bulk operations: POST /assets/bulk-delete, POST /assets/bulk-tag.

Album update: PUT /albums/{id} with UpdateAlbumHandler (title, description).

OpenAPI: utoipa annotations on all 47 endpoints + all request/response
schemas registered. Scalar UI at /scalar covers full API.

crates/api-types/src/requests.rs

@@ -91,6 +91,34 @@ pub struct RegisterAssetRequest {
     pub file_size: u64,
 }
 
+// --- Bulk ---
+
+#[derive(Debug, serde::Deserialize, utoipa::ToSchema)]
+pub struct BulkDeleteRequest {
+    pub asset_ids: Vec<uuid::Uuid>,
+}
+
+#[derive(Debug, serde::Deserialize, utoipa::ToSchema)]
+pub struct BulkTagRequest {
+    pub asset_ids: Vec<uuid::Uuid>,
+    pub tag_name: String,
+}
+
+// --- Album update ---
+
+#[derive(Debug, serde::Deserialize, utoipa::ToSchema)]
+pub struct UpdateAlbumRequest {
+    pub title: Option<String>,
+    pub description: Option<String>,
+}
+
+// --- Stack reorder ---
+
+#[derive(Debug, serde::Deserialize, utoipa::ToSchema)]
+pub struct ReorderStackRequest {
+    pub member_order: Vec<uuid::Uuid>,
+}
+
 // --- Stacks ---
 
 #[derive(Debug, serde::Deserialize, utoipa::ToSchema)]

crates/api-types/src/responses.rs

@@ -87,7 +87,7 @@ impl AssetResponse {
 #[derive(Debug, serde::Serialize, utoipa::ToSchema)]
 pub struct TimelineResponse {
     pub assets: Vec<AssetResponse>,
-    pub total: usize,
+    pub total: u64,
 }
 
 #[derive(Debug, serde::Serialize, utoipa::ToSchema)]