feat(android): add accessibility xpath audit core

[quanruzhuoxiu]

Summary

• expose a production-consistent Android Accessibility snapshot with raw XML, normalized UiNode tree, source, timing, DPR, rotation, and logical size
• add shared tree enumeration, structural XPath diagnostics, production cache candidate inspection, fresh/revisit replay, and minimal semantic overlay selection
• share Android audit metadata and schema definitions between CLI and Playground consumers

Stack

Part 1 of 3.

• base: fix/cache-xpath-replay
• next: feat/android-xpath-audit-cli

This PR does not change the production XPath candidate policy.

Validation

• pnpm exec nx build @midscene/android --skip-nx-cache
• pnpm exec nx test @midscene/android --skip-nx-cache -- tests/unit-test/page.test.ts tests/unit-test/audit-metadata.test.ts tests/unit-test/xpath-audit.test.ts tests/unit-test/cache-compatibility.test.ts
• pnpm run lint

The focused suite passed 226 tests. Vitest 3 rejects the originally suggested Jest-only --runInBand option, so the successful command omits it.

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[quanruzhuoxiu]

Superseded by #2891. The replacement stack is self-contained from main and preserves the same review layer.