Keep WASM IME visible when the canvas loses focus

[yuchanns]

Summary

• keep the active WASM IME textarea visible when browser focus moves away from the canvas
• leave real window blur/focus lifecycle handling to the existing JavaScript listeners

Root cause

Focusing the IME textarea causes Sokol to emit SAPP_EVENTTYPE_UNFOCUSED for the canvas. Treating that canvas event as a window blur immediately hides the textarea, so a mobile first-touch keyboard request is lost until a later resize or focus event reapplies the IME rectangle.

Validation

• ./bin/luamake-bin/bin/osx_arm64/luamake -compiler emcc
• mobile Playwright touch sequence confirms textarea focus occurs inside the original touch event with transient user activation
• IME composition, touch selection, scrolling, and native macOS smoke checks pass in the Miru integration

[yuchanns]

忽视这个 pr 。无语了，试用 gpt5.6 很快噌的一下就乱提 pr 了