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/postgres/202607190002_seed_pages_source_scan.sql

@@ -0,0 +1,38 @@
+-- +goose Up
+-- Earlier built-in schedules used explicit IDs, so advance the identity only
+-- when it trails either existing rows or an already-higher sequence value.
+SELECT setval(
+    pg_get_serial_sequence('w_schedules', 'id'),
+    GREATEST(
+        1,
+        COALESCE((SELECT MAX(id) FROM w_schedules), 0),
+        COALESCE((
+            SELECT sequences.last_value
+            FROM pg_sequences AS sequences
+            WHERE format('%I.%I', sequences.schemaname, sequences.sequencename)::regclass =
+                  pg_get_serial_sequence('w_schedules', 'id')::regclass
+        ), 0)
+    ),
+    TRUE
+);
+
+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 * * * *',
+    '{}',
+    TRUE,
+    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 = TRUE;