docs: update project docs and clean up redundant files
- PROGRESS.md: update to 2026-05-29 with security hardening (T-005),
4-frontend architecture, AI provider refactoring, discovery features,
landing page/referral/quota, desktop layout, admin AI management
- AGENTS.md: add AI provider list (Alibaba/NVIDIA, removed Claude/DeepL/Local),
DB-driven config, CSRF/rate-limit/CORS notes, admin_ai reload quirk
- .env.example: sync with actual config, replace deprecated providers
with current Sensenova/OpencodeGo/NVIDIA/Spark/Alibaba
- docs/PROJECT_STATUS.md: archive (fully superseded by PROGRESS.md)
- Remove generated JS files (_bing_search.js, _batch_search.js)
- Remove empty directories (data/corpus, data/models)
- Remove backend/.coverage (test artifact)
- Fix services/.gitignore to cover _bing_search.js
- Include pending AI provider DB admin feature (admin_ai, AIProvider model,
AIProviders.vue, migration) and T-008 test report
TradeMate Dev
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