fix(tui): retain interrupt confirmation setting

[Sayt-0]

Summary

• retain the parsed interrupt confirmation mode in the top-level TUI model
• pass the retained mode to initial, new, restored, and rebuilt chat pages
• normalize and propagate settings changes to existing and future pages
• add regression coverage for persisted startup state, settings application, and page recreation

Issue expectations

Expectation	Implementation
none and double-tap survive restart	Startup parses settings.interrupt_confirmation into appModel.interruptMode
New and rebuilt pages preserve the mode	chatPageOpts() passes chat.WithInterruptMode(m.interruptMode)
Settings changes affect open and future tabs	handleApplySettings() retains the normalized mode and updates every live chat page
Invalid values keep the safe default	Values are normalized through ParseInterruptMode, falling back to always
Prevent regression	Tests cover startup, existing-page propagation, future pages, and invalid values

Validation

• task build
• task test
• task lint

Closes #3993