fix(helper): report denied clipboard writes so text input can fall back

[theworker02]

Fixes #127

Problem

GestureController.setClipboard() returned true whenever setPrimaryClip() did not throw. On builds that restrict WRITE_CLIPBOARD to the foreground via AppOps (the reported OPPO PMT110 shows WRITE_CLIPBOARD: foreground), ClipboardService drops the write silently (op=30 result=false). The host then sent KEYCODE_PASTE, reported success, and never reached the ADBKeyboard fallback, so Chinese text was never entered.

Change

• GestureController.setClipboard() now checks the android:write_clipboard AppOps mode before writing:
  • MODE_ALLOWED / MODE_DEFAULT: write as before.
  • MODE_FOREGROUND: write only if the helper process importance is foreground or foreground-service; otherwise return false.
  • MODE_IGNORED / MODE_ERRORED: return false.
  • If the op name is unknown on a build, it keeps the previous optimistic behaviour.
• A false result already makes AndroidAdbDriver.input_text() skip the paste and fall through to the ADBKeyboard broadcast and native input text, so no host-side logic change is needed.
• Added test_android_input_text_falls_back_to_adbkeyboard_when_clipboard_rejected, which pins that a rejected clipboard write never sends KEYCODE_PASTE and delivers the text via ADB_INPUT_B64.

Testing

• uv run pytest tests/unit/test_drivers.py passes (6 tests).
• ruff format --check and ruff check pass on the changed test file.
• I could not build the helper APK or test on a device locally (no Android SDK), so the Java change is compile-unverified. It only uses public APIs available at minSdk 24 (checkOpNoThrow below API 29, unsafeCheckOpNoThrow from API 29, ActivityManager.getMyMemoryState). A device check on a build with WRITE_CLIPBOARD: foreground would be appreciated.
• The full make test run on Windows shows failures in unrelated agent/CLI tests. tests/unit/agents/flash/test_turn_index_snapshot.py fails the same way on unmodified main (see test(flash): mock VisualStepSummarizer in test_turn_index_snapshot for offline execution #32 / fix(tests): mock VisualStepSummarizer in test_turn_index_snapshot #35).

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