feat(core): allow keyboard press without a locate target

[quanruzhuoxiu]

Summary

• allow the recommended aiKeyboardPress signature to receive undefined as its locate argument
• omit locating and the preliminary click when the shortcut should operate on the currently focused element
• guide the planner to omit locate for Copy or Cut after text has already been selected
• document the API in English and Chinese while preserving eager model configuration validation
• cover direct Playwright and Puppeteer calls and an aiAct-planned targetless Backspace with a generated report

Scope

This PR targets main directly and contains only the optional-locate API, planner guidance, documentation, and targetless tests. It does not contain the focusElement implementation or browser-side Cut command mapping from #2962.

Validation

• pnpm run lint
• pnpm exec nx build @midscene/core
• pnpm exec nx build @midscene/web
• pnpm exec tsc --noEmit -p packages/web-integration/tsconfig.json
• pnpm test -- tests/unit-test/action-keyboard-press.test.ts tests/unit-test/prompt/prompt.test.ts in packages/core (46 tests passed)
• PUPPETEER_EXECUTABLE_PATH='/Applications/Google Chrome.app/Contents/MacOS/Google Chrome' pnpm test -- tests/unit-test/agent-keyboard-press-targetless-e2e.test.ts in packages/web-integration (2 tests passed)

Merge order

Merge this PR into main first. #2962 is an independent browser-side follow-up.

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