Code execution consent dialog

Modal shown the first time the user invokes Run on a runnable fenced block in rendered/split markdown preview while consent has not yet been recorded.

Behaviour

• Persistence: Settings.code_execution_consent_acknowledged (default false) in config.json.
• Preview gate: CodeExecutionUi carries consent_acknowledged from settings. run_button_visible shows Run for shell/Python fences when allow_* passes and either the master toggle is on or consent is still unset — so users can discover execution without opening Settings first.
• Defer spawn: On Run click, if enable_code_execution && code_execution_consent_acknowledged both hold in the snapshot, spawn_run runs immediately as before. Otherwise the snippet is queued as PendingCodeRun via egui temp storage and drained into UiState at the start of render_dialogs.
• Settings shortcut: Turning Allow code execution from Off→On in Settings sets consent immediately (src/ui/settings.rs) without showing the modal.

Buttons

Action	Effect
Enable & run	Master on, consent true, save settings, spawn_run for queued payload, attach RunHandle under the block id
Just enable	Master on, consent true, save settings, discard queued run
Cancel / Esc	No settings change, discard queued run

Initial keyboard focus is on Cancel. Strings live under dialog.code_execution_consent.* in locales/en.yaml.

References

• src/app/dialogs.rs — window rendering and actions
• src/markdown/widgets.rs — Run click branch
• src/markdown/code_execution.rs — push_pending_code_execution_consent, take_pending_code_execution_consent, run_button_visible
• src/config/settings.rs — code_execution_consent_acknowledged