Initial commit: @b2c/first_page HarmonyOS stage-mode HAR

## Repository
- HarmonyOS stage-mode HAR module, consumed by host app
- No standalone build — hvigorw, oh_modules, and ../biz_quote absent here

## Architecture
### Feed Cards
- FirstPage.createNodeView dispatches cards by FirstPageConstant.KEY_*
- Card config from first_page_cards_config.json loaded by FirstPageCardsConfigLoader
- Public entrypoint: Index.ets

### Market Ranking (src/main/ets/market-ranking/)
- HTTP: MarketRankingDataFetcher fetches recommend_futures contracts
- HQ: MarketRankingHqRequestClient subscribes via 4106/frame 2201/scenario qht_qihuo_sort
- TCP reconnect rebuilds subscription from original HTTP contract list
- Async callbacks guarded by request/subscription versions

### Other Cards
- HotList, CommodityOptions, AiDiagnosis, AiRiseFall, SelfSelectedStock, CustomEntryList, FourEntryList
- Each has DataFetcher + HQ request client + NodeComponent

## Key Changes (from CardHarmonyOS reference)
- Added MetricId, PeriodId, SortOrder enums (MarketRankingModels.ets)
- Replaced string comparisons with enum switches in thirdColumnTitle/Value/Color
- Removed redundant undefined guards in thirdColumnColor/priceColor, delegated to riseFallColor
- Inlined priceColor(), use riseFallColor directly
- Tab bar Stack.height(30), Alignment.End (reverted from 46/TopEnd)
- Name column fontWeight removed (default regular)

src/main/resources/en_US/element/string.json

@@ -0,0 +1,8 @@
+{
+  "string": [
+    {
+      "name": "page_show",
+      "value": "page from package"
+    }
+  ]
+}