vibium eval shows empty "script exception:" message instead of the real error

[Jhoan0714]

Description

When a JavaScript expression fails during CLI vibium eval or MCP browser_evaluate, Vibium reports a generic error with no useful detail:

Error: failed to evaluate: script exception:

The browser does throw a real exception (e.g. SecurityError, ReferenceError), but Vibium fails to read it from the WebDriver BiDi response and surfaces an empty message instead.

Steps to Reproduce

1. Run a script that throws on the default page (about:blank - lazy launch):

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

   Or navigate first and throw a reference error:

   vibium go "https://example.com"
   vibium eval "undefinedVariable"

Expected Behavior

The CLI should show the actual JavaScript exception message, for example:

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

or:

Error: failed to evaluate: script exception: ReferenceError: undefinedVariable is not defined

Actual Behavior

Error: failed to evaluate: script exception:

The message after script exception: is always empty, making debugging impossible.

Root Cause

CLI and MCP evaluation go through browser_evaluate → h.client.Evaluate() in clicker/internal/bidi/script.go.

When a script throws, the WebDriver BiDi spec returns type: "exception" with details in exceptionDetails (including text, lineNumber, stackTrace), not in result:

{
  "type": "exception",
  "exceptionDetails": {
    "text": "SecurityError: Failed to read the 'localStorage' property...",
    "lineNumber": 1,
    "columnNumber": 1
  }
}

Vibium only parses type and result, and builds the error from the wrong field:

// clicker/internal/bidi/script.go
if evalResult.Type == "exception" {
    return nil, fmt.Errorf("script exception: %s", string(evalResult.Result))
}

evalResult.Result is empty for exception responses, so the error message is blank.

Impacted Operations

• CLI: vibium eval
• MCP: browser_evaluate
• Any daemon/MCP handler that uses bidi.Client.Evaluate() or bidi.Client.CallFunction() in clicker/internal/bidi/script.go

Proposed Fix

In clicker/internal/bidi/script.go, parse exceptionDetails when type == "exception" and use exceptionDetails.text (and optionally line/stack) in the error message. Apply the same fix to both Evaluate() and CallFunction().