feat: enhance screenshot functionality to restore viewport size and support CDP overrides

[rajarshidattapy]

Description

Fixes a screenshot viewport leak: --width/--height overrides were permanently pinning the viewport on real-window (stealth) sessions.

applyScreenshotViewport returned page.viewportSize() as the value to restore, but that is null when the Cloak context uses the real OS window (viewport: null). The finally guard if (previousViewport) then treated null as "nothing to restore" and skipped it, so the override (e.g. 375×812) stuck for every subsequent command in that session.

Replaced the helper with captureScreenshot(page, context, command) that restores in both cases:

• Emulated viewport (non-null): override via setViewportSize, restore the prior size in finally — unchanged behavior.
• Real-window context (viewportSize() === null): setViewportSize can't return to a windowed state, so it overrides reversibly via CDP Emulation.setDeviceMetricsOverride and clears it with Emulation.clearDeviceMetricsOverride in finally — fully restoring the real window. Reuses the existing context.newCDPSession pattern.

Added a regression test for the previously-uncovered null-viewport path (asserts setViewportSize is never called, the CDP override is applied and then cleared/detached).

Related issue: #120

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Adapter Notes

N/A — runtime fix, no adapter or command-discoverability changes.

• Updated generated or lean docs when command discoverability changed
• Used positional args for the command's primary subject unless a named flag is clearly better
• Normalized expected adapter failures to CliError subclasses instead of raw Error

Screenshots / Output

$ npx vitest run src/browser/runtime/local-cloak/provider.test.ts

Test

Test Files 1 passed (1)
Tests 25 passed (25)

• npx tsc --noEmit clean on src.

[github-actions]

🟢 No documentation gap found — medium confidence

The automated review found no documentation gap in the supplied changes.

This review is advisory and does not block merging.