fix(webrtc): 接入 WebRTC 147 header overlay

[iamsyc]

Summary

• replace the remote stasel/WebRTC source package with a checked WebRTC 147 binary target plus local header wrapper
• add M147 header overlay source docs and SHA256 coverage
• extend static and release smoke gates for overlay and binary architecture validation

Validation

• swift package resolve
• ROOT_DIR="$PWD" TOOL_ROOT="$PWD" scripts/ci/static.sh
• swift test --scratch-path .ai-tmp/swift-test-webrtc147-full
• ROOT_DIR="$PWD" TOOL_ROOT="$PWD" scripts/ci/xcode.sh --action build --configuration Debug --out-dir .ai-tmp/xcode-build-webrtc147-audit
• ROOT_DIR="$PWD" TOOL_ROOT="$PWD" scripts/ci/release_smoke.sh --arch arm64 --out-dir .ai-tmp/release-smoke-webrtc147-arm64-audit
• ROOT_DIR="$PWD" TOOL_ROOT="$PWD" scripts/ci/release_smoke.sh --arch x86_64 --out-dir .ai-tmp/release-smoke-webrtc147-x86_64-audit

[github-actions]

CI Summary

Run: Open

Check	Status	Details
Change Scope	ui_code	code=true, ui=true
Dependency Review	success	code PR gate; high and critical vulnerabilities block
Static Checks	success	actionlint, shellcheck, shfmt, SwiftFormat, SwiftLint, action pinning
Unit Tests	success	Swift tests: 538 Go packages: 2 Reason: passed Artifact: unit-gate
Xcode Build	success	Debug build with zero warning scan Artifact: xcode-build
UI Smoke	success	Failure classification is written by ui-smoke-summary.json in each artifact. Artifacts: ui-smoke-baseline, ui-smoke-permissionDenied, ui-smoke-rebuildFailed
Release Smoke	success	Artifacts: release-smoke-arm64, release-smoke-intel64 Release verify summaries are produced by release.yml before publishing.
Artifacts	link	Open artifacts
CI Gate	success	single branch protection check