Add queue management API and database queries

- Add 7 new database queries for queue management
- GetStuckSyncQueueItems - Detect stuck items
- GetSyncQueueStats - Queue statistics
- GetNextRetryTime - Exponential backoff calc
- ListAllSyncQueueItems - Admin view
- IncrementSyncQueueAttempts - Retry counter
- Add queue handler with 7 REST endpoints
- GET /api/queue/devices/:id/stats - Queue statistics
- GET /api/queue/devices/:id/items - List device queue
- POST /api/queue/items/:id/retry - Retry failed item
- DELETE /api/queue/items/:id - Delete queue item
- DELETE /api/queue/devices/:id/clear - Clear device queue
- GET /api/queue/items - List all items (admin)
- Add full user/admin access control

internal/database/queries/queries.sql

@@ -305,6 +305,12 @@ UPDATE users SET email = $2, updated_at = NOW() WHERE id = $1;
 -- name: UpdatePassword :exec
 UPDATE users SET password_hash = $2, updated_at = NOW() WHERE id = $1;
 
+-- name: UpdateUserMaxDevices :exec
+UPDATE users SET max_devices = $2, updated_at = NOW() WHERE id = $1;
+
+-- name: CountUserDevices :one
+SELECT COUNT(*) FROM devices WHERE user_id = $1;
+
 -- name: DeleteUser :exec
 DELETE FROM users WHERE id = $1;
 
@@ -720,6 +726,64 @@ DELETE FROM sync_queue WHERE id = $1;
 -- name: ClearDeviceSyncQueue :exec
 DELETE FROM sync_queue WHERE device_id = $1;
 
+-- name: GetFailedSyncQueueItems :many
+SELECT * FROM sync_queue
+WHERE status = 'failed' AND attempts < max_attempts
+ORDER BY priority ASC, created_at ASC
+LIMIT $1;
+
+-- name: GetStuckSyncQueueItems :many
+SELECT * FROM sync_queue
+WHERE status = 'processing' AND created_at < NOW() - INTERVAL '1 hour'
+ORDER BY priority ASC, created_at ASC;
+
+-- name: IncrementSyncQueueAttempts :one
+UPDATE sync_queue
+SET
+    attempts = attempts + 1,
+    status = CASE 
+        WHEN attempts + 1 >= max_attempts THEN 'failed'
+        ELSE 'pending'
+    END,
+    error_message = $2
+WHERE id = $1
+RETURNING *;
+
+-- name: GetSyncQueueStats :one
+SELECT
+    COUNT(*) FILTER (WHERE status = 'pending') as pending_count,
+    COUNT(*) FILTER (WHERE status = 'processing') as processing_count,
+    COUNT(*) FILTER (WHERE status = 'failed') as failed_count,
+    COUNT(*) FILTER (WHERE status = 'completed') as completed_count,
+    COUNT(*) as total_count
+FROM sync_queue
+WHERE device_id = $1;
+
+-- name: ListAllSyncQueueItems :many
+SELECT 
+    sq.*,
+    d.device_name,
+    d.device_type,
+    u.email as user_email,
+    mi.title as media_title
+FROM sync_queue sq
+JOIN devices d ON sq.device_id = d.id
+JOIN users u ON d.user_id = u.id
+LEFT JOIN media_items mi ON sq.media_item_id = mi.id
+ORDER BY sq.priority ASC, sq.created_at DESC
+LIMIT $1 OFFSET $2;
+
+-- name: GetNextRetryTime :one
+SELECT 
+    CASE 
+        WHEN attempts = 0 THEN NOW()
+        WHEN attempts = 1 THEN NOW() + INTERVAL '1 minute'
+        WHEN attempts = 2 THEN NOW() + INTERVAL '5 minutes'
+        WHEN attempts = 3 THEN NOW() + INTERVAL '15 minutes'
+        WHEN attempts = 4 THEN NOW() + INTERVAL '1 hour'
+        ELSE NOW() + INTERVAL '24 hours'
+    END as next_retry_time;
+
 -- Conflict Resolution
 -- name: CreateSyncConflict :one
 INSERT INTO sync_conflicts (media_item_id, user_id, conflict_type, conflict_data)