feat: add interactive controls (button, switch, text input)

[janicduplessis]

Adds three controls below the existing title and subtitle so agents can tap and type while verifying changes, and Stim Desktop records those as agent actions: a "Tap me" button with a counter, a "Dark accent" switch that recolors the card, and a "Your name" input that echoes "Hello, ". Each has an accessibility label and a testID, so agent-device snapshots name them. Colors for the button, switch track, card and input border live in theme.js (buttonColor, buttonTextColor, accentColor, darkAccentColor, inputBorderColor). No new dependencies; the title, subtitle, titleColor, backgroundColor, the [stim:tutorial] log line, the readiness signals and expo.extra.stimTutorial are unchanged.

Before	After

How it was verified

• Device: stim-tutorial-controls-wt (iPhone 18 Pro, iOS 27.0)
• Readiness: Stim waited for the app to report ready (4.3s verification)
• Build: 1m51s, from Stim's native build cache (JS-only change)
• Logs: stim logs --errors returned no records. stim logs --source agent showed the snapshot, three taps on "Tap me", the switch toggle and the fill of the name input; the app then showed "Tapped 3 times" and "Hello, Janic".

Built and verified with Stim.

[github-actions]

Nice change, @janicduplessis! Thanks for trying Stim. This repo is the Stim tutorial app, so we close tutorial PRs automatically. See you in your next worktree.

If Stim saved you some time, a ⭐ on appandflow/stim would make our day.