feat(effects): surface error message and stack trace in effects panel

[vineethwilson15]

Closes #41

When an NgRx effect throws, the effects panel now shows the error message
inline and a collapsible stack trace — no more opening the browser console.

Changes:

• core.models.ts: add errorMessage/errorStack to DevToolEffectEventPayload
• actions-interceptor.service.ts: extract and forward error details in EFFECT_EVENT messages
• effects-panel.models.ts: add errorMessage/errorStack to EffectEventMessage and EffectExecution
• effects-panel.component.ts: populate error fields in effectExecutions computed signal
• effects-panel.component.html: render error message inline; collapsible stack trace via <details>
• effects-panel.component.scss: styles for error message and stack trace
• actions-interceptor.service.spec.ts: 3 new unit tests covering error forwarding

[adxdits]

Hello, thanks for contributing 👑 will review it next week

[adxdits]

Great 👍 my only suggestion would be that in actions-interceptor.service.ts errorMessage and errorStack are extracted and sent for every effect event, even non-error ones (where they'll be undefined). This works correctly due to JSON.stringify omitting undefined values, but it would be slightly cleaner to only compute them when event.lifecycle === 'error'

[vineethwilson15]

Thanks for the feedback and for merging! That's a fair point — computing errorMessage/errorStack unconditionally is harmless but unnecessarily runs for non-error events.

Happy to open a small follow-up refactor PR that moves the extraction inside an if (event.lifecycle === 'error') guard. Let me know if you'd like that, or if you'd prefer to address it as part of a future cleanup.