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/mobile_cloud_catalog_sample.txt

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+# 移动云市场
+AI应用专区
+数据大模型
+覆盖智能客服、办公提效、数据分析等场景能力。