feat(imports): add real pricing and subscription collectors

Add plan catalog and subscription schema support, seed baselines, and real importers for core domestic subscriptions plus stable official pricing sources.

This commit also hardens the shared fetch layers so the importers can support live collection and database writes instead of relying on manual placeholders alone.

scripts/testdata/zhipu_coding_plan_promotion_sample.txt

@@ -0,0 +1,3 @@
+# 限时活动
+GLM Coding Plan 编码畅享计划，低至20元/月，适用于 Claude Code、Cline、Continue、Open Code 等平台。
+首单 9 折优惠，新老用户均可参与。