Add independent controls for TUI visual effects (#46832)

## What changed

Replace `tui.whimsy` with `[tui.effects]` preferences for `starfield`, `shimmer`, `welcome`, `effort`, `progress`, and `title`. Each defaults to `true` and remains subordinate to the `tui.animations` master switch.

Wire the preferences into composer effects, welcome artwork, status and loading text, progress indicators, and terminal-title animations. For example, disable shimmering text while keeping progress animations:

```toml
[tui.effects]
shimmer = false
```

Keep retired `tui.whimsy` entries loadable but ignore their value. Update the configuration schema to expose the new preferences.

## Testing

Add and extend coverage for independent shimmer and progress effects, master-switch precedence, welcome and starfield controls, terminal-title blinking, and strict configuration loading with the retired setting.

GitOrigin-RevId: 28b37ba52872133b8954543cabe9ff424147f1c5

codex-rs/tui/src/startup_draft.rs

@@ -505,6 +505,7 @@ fn startup_draft_bottom_pane(
             placeholder_text: "Ask Codex to do anything".to_string(),
             disable_paste_burst: false,
             animations_enabled: crate::system_motion::mode() == crate::motion::MotionMode::Animated,
+            effects: Default::default(),
             skills: None,
         },
         ChatComposerConfig::plain_text(),