fix(server): guard invalid JSON in PageBinding.dispatch

[SebTardif]

Summary

PageBinding.dispatch parsed the binding payload with JSON.parse outside the existing try/catch. A malformed payload from the page (or a corrupted protocol message) threw an uncaught SyntaxError and aborted the binding pipeline.

Fix

Parse the payload in a dedicated try/catch. On invalid JSON, log via debugLogger and return. When parse succeeds, the existing try/catch still delivers binding errors to the page with name/seq.

Evidence (red / green)

# Red (before fix)
SyntaxError: Expected property name or '}' in JSON at position 1
  await pageImpl.onBindingCalled('{not-valid-json', context);

# Green (after fix)
1 passed — page continues to evaluate after bad payload
page-expose-function.spec.ts: 22 passed (chromium-page)

Test plan

• New test: invalid binding payload does not crash
• Full page-expose-function.spec.ts on chromium-page