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/youdao_pricing_sample.txt

@@ -0,0 +1,36 @@
+DeepSeek V4 Flash
+DeepSeek
+上下文长度 1M
+输入:¥0.5
+输出:¥2
+查看详情
+DeepSeek V4 Pro
+DeepSeek
+上下文长度 128K
+输入:¥2
+输出:¥8
+查看详情
+Kimi K2.6
+Kimi
+上下文长度 262K
+输入:¥4
+输出:¥16
+查看详情
+MiniMax M2.5
+Minimax
+上下文长度 1M
+输入:¥1
+输出:¥8
+查看详情
+GLM-5
+Zhipu
+上下文长度 128K
+输入:¥1
+输出:¥3
+查看详情
+Qwen-3.6-Plus
+Qwen
+上下文长度 256K
+输入:¥0.8
+输出:¥3.2
+即将上线