fix(tui): ignore lock/private-use key events in text inputs

[danix800]

Issue for this PR

Closes #16310

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

VS Code 1.110 started reporting CapsLock through kitty keyboard protocol in a way that surfaced as private-use text (U+E00E) in OpenCode TUI inputs.

This PR adds a shared input guard that blocks lock keys (capslock, numlock, scrolllock) and private-use Unicode key events from being inserted as text. It wires the guard into all editable TUI text inputs used in prompts and dialogs, and adds tests for both BMP and supplementary private-use code points.

How did you verify your code works?

• Reproduced locally in VS Code integrated terminal: CapsLock no longer inserts stray characters.
• Ran bun run typecheck in packages/opencode.
• Ran bun test test/cli/tui in packages/opencode.

Screenshots / recordings

N/A (TUI input handling change).

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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[github-actions]

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