feat: add findInFrames() and fillForm() helpers for iframe support

[MarcinDudekDev]

Summary

Add two new client methods to simplify working with iframes (Stripe, PayPal, embedded widgets):

• findInFrames(name, selector, options) - Searches all frames (main + nested) for an element. Returns the element, frame reference, and debug info. Auto-detects Stripe/PayPal iframes in the frame info.

• fillForm(name, fields, options) - Smart form filling that finds fields by label, name, placeholder, or aria-label across all frames. Supports auto-submit option.

Problem

When automating payment forms or embedded widgets, selectors often work in DevTools but fail in Playwright scripts because the element is inside an iframe. Manually iterating through page.frames() is tedious and error-prone.

Solution

These helpers abstract away the frame iteration logic:

// Before: manual frame iteration
for (const frame of page.frames()) {
  try {
    const el = await frame.waitForSelector('input[name="cardnumber"]', { timeout: 500 });
    if (el) { /* found it */ }
  } catch { /* not in this frame */ }
}

// After: one-liner
const { element, frameInfo } = await client.findInFrames("checkout", 'input[name="cardnumber"]');

Test plan

• TypeScript compiles without errors
• Existing tests pass (bun test - 9 tests pass)
• Manual test: findInFrames finds elements in main frame
• Manual test: findInFrames finds elements in iframes
• Manual test: fillForm fills fields across main frame and iframes
• Documentation added to SKILL.md

🤖 Generated with Claude Code