feat(pages): 增加来源扫描与自动更新

为 GitHub latest 来源增加五分钟 scanner、按来源间隔检查、精确 revision 自动发布与租约恢复。\n记录退避和投递统计，并为 PostgreSQL 与 SQLite 幂等创建内部排程。

internal/db/migrator/goose/sqlite/202607190002_seed_pages_source_scan.sql

@@ -0,0 +1,21 @@
+-- +goose Up
+INSERT INTO w_schedules (name, task_type, cron, payload, is_active, created_at, updated_at)
+SELECT
+    'OpenFlare Pages 部署源扫描',
+    'of_pages_source_scan',
+    '*/5 * * * *',
+    '{}',
+    1,
+    CURRENT_TIMESTAMP,
+    CURRENT_TIMESTAMP
+WHERE NOT EXISTS (
+    SELECT 1 FROM w_schedules WHERE task_type = 'of_pages_source_scan'
+);
+
+-- +goose Down
+DELETE FROM w_schedules
+WHERE task_type = 'of_pages_source_scan'
+  AND name = 'OpenFlare Pages 部署源扫描'
+  AND cron = '*/5 * * * *'
+  AND payload = '{}'
+  AND is_active = 1;