fix(tui): default queue keybind to ctrl+shift+return for WezTerm

[henry701]

Summary

• Changes the default TUI queue keybind from alt+return to ctrl+shift+return so terminals like WezTerm that capture Alt+Enter no longer block queueing.
• The binding was already configurable; this PR only updates the default and clarifies the keybind description.

Config override

Set a custom queue binding in your TUI config:

{
  "keybinds": {
    "input_queue": "alt+return"
  }
}

Or in migrated tui.json under the same input_queue key.

Validation

• bun test test/cli/run/runtime.boot.test.ts test/cli/run/prompt.shared.test.ts test/cli/run/runtime.queue.test.ts (from packages/opencode)
• bun typecheck (monorepo)