Stop toolbar taps from resummoning the dismissed keyboard (#200)

[Renakoni]

Closes #200 — toolbar taps no longer resummon a keyboard the user just dismissed.

The chain, established on API 35

1. Dismissing the IME with Back does not blur Muya: CDP still reports the editor as document.activeElement.
2. Toolbar controls deliberately prevent pointer/mouse defaults so formatting taps do not steal focus while typing.
3. Android Chromium re-shows the IME after a page-consumed tap when an editable still owns focus.
4. The panel-menu selection replay can also focus the editable through Selection.addRange().

Before this PR, expand, collapse, the panel switcher, and its options all reproduced the unwanted keyboard return. The API 35 device matrix verified that those navigation taps stay keyboard-free after the guard, while expanding with the IME already open preserves focus and the keyboard.

Implementation

• A capture-phase toolbar pointerdown guard blurs editor-owned focus only when the IME is explicitly known to be hidden. Navigation taps then have no focused editable to resummon the keyboard for; edit commands restore their caret/focus through their existing Muya paths.
• Android now provides the authoritative state from WindowInsetsCompat.Type.ime() through the existing AndroidSelection bridge. It publishes retained imeVisibilityChanged events and an initial getImeVisibility() snapshot. Listener-first installation plus an event-version gate prevents a late snapshot from overwriting a newer event.
• Floating keyboards and rotation no longer depend on viewport geometry: native IME insets remain authoritative even without adjustResize.
• Non-native/browser environments keep the viewport estimator as a fallback, now with unknown | hidden | visible states. Its first sample and every post-rotation sample are unknown; unknown means no intervention, never blur.
• The panel-menu selection replay runs only while the editor already owns focus, so it cannot undo the guard.

Verification

• Web unit suite: 83 files / 699 tests green; estimator coverage includes first-sample uncertainty, keyboard-sized shrink/recovery, sub-threshold changes, rotation with the IME already open, in-place baseline growth, and no-resize floating-keyboard behavior.
• Mobile toolbar WebView e2e: 40/40 green. New native-bridge cases verify:
  • a visible no-resize floating keyboard preserves editor focus;
  • hidden-IME formatting and undo/redo each execute the capture blur and then restore editor focus from a collapsed caret;
  • a hidden-IME table structure command follows the same blur/restore contract.
• vue-tsc -b, production build, focused ESLint, Android JVM tests, Java compilation, and assembleDebug all pass locally.
• The previous API 35 device matrix covered the real soft-keyboard navigation behavior. No ADB device was attached for the final d131e7e follow-up; current-head GitHub Web Quality, Android Connected Tests, and Android Debug Build were triggered on push.