feat(enterprise): add frontend lease heartbeat

[Gracker]

Summary

• add POST /api/tp/:leaseId/heartbeat for frontend holder visibility heartbeats
• reacquire the scoped frontend holder when the window holder disappeared but the lease remains acquirable
• document the heartbeat proxy target and align frontend visibility TTLs with the current lease store policy

Tests

• PATH="/Users/chris/.nvm/versions/node/v24.15.0/bin:/Users/chris/.codex/tmp/arg0/codex-arg0Ggjp4H:/Users/chris/.nvm/versions/node/v20.19.0/lib/node_modules/@openai/codex/node_modules/@openai/codex-darwin-arm64/vendor/aarch64-apple-darwin/path:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.config/kaku/zsh/bin:/Users/chris/.opencode/bin:/Users/chris/.bun/bin:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.nvm/versions/node/v20.19.0/bin:/opt/homebrew/share/google-cloud-sdk/bin:/Users/chris/.local/bin:/Users/chris/.local/bin:/Users/chris/.codeium/windsurf/bin:/Library/Frameworks/Python.framework/Versions/3.12/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pkg/env/active/bin:/opt/pmk/env/global/bin:/Library/Apple/usr/bin:/usr/local/go/bin:/Users/chris/.cargo/bin:/Users/chris/tools/Android-sdk/platform-tools/:/Users/chris/tools/TTDeDroid/bin:/Users/chris/tools/depot_tools:/Users/chris/tools/flutter/flutter/bin:/Applications/Warp.app/Contents/Resources/bin" npx jest --runInBand --forceExit src/routes/tests/traceProcessorProxyRoutes.test.ts
• PATH="/Users/chris/.nvm/versions/node/v24.15.0/bin:/Users/chris/.codex/tmp/arg0/codex-arg0Ggjp4H:/Users/chris/.nvm/versions/node/v20.19.0/lib/node_modules/@openai/codex/node_modules/@openai/codex-darwin-arm64/vendor/aarch64-apple-darwin/path:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.config/kaku/zsh/bin:/Users/chris/.opencode/bin:/Users/chris/.bun/bin:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.nvm/versions/node/v20.19.0/bin:/opt/homebrew/share/google-cloud-sdk/bin:/Users/chris/.local/bin:/Users/chris/.local/bin:/Users/chris/.codeium/windsurf/bin:/Library/Frameworks/Python.framework/Versions/3.12/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pkg/env/active/bin:/opt/pmk/env/global/bin:/Library/Apple/usr/bin:/usr/local/go/bin:/Users/chris/.cargo/bin:/Users/chris/tools/Android-sdk/platform-tools/:/Users/chris/tools/TTDeDroid/bin:/Users/chris/tools/depot_tools:/Users/chris/tools/flutter/flutter/bin:/Applications/Warp.app/Contents/Resources/bin" npm run typecheck
• PATH="/Users/chris/.nvm/versions/node/v24.15.0/bin:/Users/chris/.codex/tmp/arg0/codex-arg0Ggjp4H:/Users/chris/.nvm/versions/node/v20.19.0/lib/node_modules/@openai/codex/node_modules/@openai/codex-darwin-arm64/vendor/aarch64-apple-darwin/path:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.config/kaku/zsh/bin:/Users/chris/.opencode/bin:/Users/chris/.bun/bin:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.nvm/versions/node/v20.19.0/bin:/opt/homebrew/share/google-cloud-sdk/bin:/Users/chris/.local/bin:/Users/chris/.local/bin:/Users/chris/.codeium/windsurf/bin:/Library/Frameworks/Python.framework/Versions/3.12/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pkg/env/active/bin:/opt/pmk/env/global/bin:/Library/Apple/usr/bin:/usr/local/go/bin:/Users/chris/.cargo/bin:/Users/chris/tools/Android-sdk/platform-tools/:/Users/chris/tools/TTDeDroid/bin:/Users/chris/tools/depot_tools:/Users/chris/tools/flutter/flutter/bin:/Applications/Warp.app/Contents/Resources/bin" npm run test:core
• PATH="/Users/chris/.nvm/versions/node/v24.15.0/bin:/Users/chris/.codex/tmp/arg0/codex-arg0Ggjp4H:/Users/chris/.nvm/versions/node/v20.19.0/lib/node_modules/@openai/codex/node_modules/@openai/codex-darwin-arm64/vendor/aarch64-apple-darwin/path:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.config/kaku/zsh/bin:/Users/chris/.opencode/bin:/Users/chris/.bun/bin:/Users/chris/.antigravity/antigravity/bin:/Users/chris/.nvm/versions/node/v20.19.0/bin:/opt/homebrew/share/google-cloud-sdk/bin:/Users/chris/.local/bin:/Users/chris/.local/bin:/Users/chris/.codeium/windsurf/bin:/Library/Frameworks/Python.framework/Versions/3.12/bin:/opt/homebrew/bin:/opt/homebrew/sbin:/usr/local/bin:/System/Cryptexes/App/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/local/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/bin:/var/run/com.apple.security.cryptexd/codex.system/bootstrap/usr/appleinternal/bin:/opt/pkg/env/active/bin:/opt/pmk/env/global/bin:/Library/Apple/usr/bin:/usr/local/go/bin:/Users/chris/.cargo/bin:/Users/chris/tools/Android-sdk/platform-tools/:/Users/chris/tools/TTDeDroid/bin:/Users/chris/tools/depot_tools:/Users/chris/tools/flutter/flutter/bin:/Applications/Warp.app/Contents/Resources/bin" npm run verify:pr

[Gracker]

已通过 commit 67856ec (merge) + 023a84a (frontend rebuild) 合入 main，关闭此 PR。