fix: show script exception text instead of empty message

[Jhoan0714]

Summary

This PR fixes #221 — when vibium eval or MCP browser_evaluate runs JavaScript that throws, the CLI previously reported an empty error:

Error: failed to evaluate: script exception:

The browser did throw a real exception, but bidi.Client read the wrong field from the WebDriver BiDi response. This change parses exceptionDetails.text so users see the actual JavaScript error message.

Why this matters

• Makes vibium eval debuggable when scripts fail (wrong variable, SecurityError on localStorage, etc.)
• Same fix applies to MCP browser_evaluate and any path using CallFunction() through the BiDi client
• Aligns with existing correct handling in parseScriptResult() (clicker/internal/api/helpers.go), which already reads exceptionDetails

Validation

Before fix:

vibium eval "localStorage.setItem('key', 'value')"

Error: failed to evaluate: script exception:

After fix:

Error: failed to evaluate: script exception: SecurityError: Failed to read the 'localStorage' property from 'Window': Access is denied for this document.

Note: rebuild and restart the daemon (vibium daemon stop && vibium daemon start) to load the new binary.