fix: keep fitting input values visible and record bare Delete/Backspace hotkeys

[kirillDevPro]

What & why

• Input values. A single-line input whose value fits the field could scroll it out of view and render blank. The field now keeps a fitting value visible; a regression test uses the platform caret width. Mirror metadata for input/text_area refreshed in the same PR.
• Hotkey capture. The hotkey recorder ignored a bare Delete or Backspace, so those keys could not be bound (needed by MoonTerminal's Delete-removes-figure action). They are now recorded as bindings.

How to verify

Local, all guardrail steps: cargo fmt --all -- --check, cargo check -p moon-ui-gallery, cargo test -p moon-ui-components, cargo test -p moon-ui-gallery, cargo xtask component-audit --check-baseline, cargo xtask component-api --check-baseline, cargo xtask component-mirror --donor-root vendor/longbridge-gpui-component-ui-src --check-baseline all green.