refactor: add XHS-shaped content platform interface

[IRONICBo]

Summary

• add an XHS-shaped ContentPlatform contract for get_notes, search, author_scan, and page_state
• expose common XHS request schemas and product defaults for note limits, comments, preview, media download, OCR, and local ASR
• select adapters by site_id through SiteSpec.content_platform without platform branches in shared dispatch code
• generate the common agent tool surface from adapter capabilities and hide unsupported operations
• implement XHS as the reference adapter and preserve the existing XHS login and rate-limit tools
• register the existing Douyin card search and page-state tools as a capability-limited adapter pending its full implementation PR
• replace hosted audio transcription with a local Qwen3-ASR 0.6B Int8 worker, CLI and desktop model installation, verified release assets, and timeout recovery

Design

• XHS owns the upper-layer vocabulary and effective-input behavior
• platform adapters own URL contracts, navigation, extraction, native entity fields, and canonical aliases
• ContentCapabilities reports full search, author scan, filters, comments, replies, media, OCR, ASR, history, and artifact support
• platform-specific CLI commands remain compatible while interactive agents receive the common four-tool surface

Validation

• cargo check -p socai-cli
• cargo check -p socai-asr -p socai-core -p socai-cli -p socai_app
• cargo test -p socai-core --lib — 99 passed, 0 failed, 2 ignored
• pnpm run build
• actual WAV and XHS MP4 transcription with the installed local model
• CDP endpoint discovery skips stale conventional ports and reconnects to another live existing browser endpoint
• macOS arm64, macOS x86_64, and Windows x86_64 sherpa-onnx archives verified against pinned SHA-256 values
• rustfmt --edition 2021 --check on changed Rust files
• git diff --check
• two-pass automated review completed with no remaining findings

[vercel]

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[IRONICBo]

按当前实现边界撤回公共 ContentPlatform 抽象。TikTok 和 Douyin 分别沿用现有 site 模块结构接入，XHS 保持不变；本地 Whisper small ASR 独立提交。