Auto-start the OAuth connect after adding a custom connector (skip the separate 'Connect' click)

### Summary

Follow-up to #74 (deep-link prefill, thank you — it works great). After a user **adds** a custom connector, it lands in the list as *not connected*, and they still have to click **Connect** to actually run the OAuth flow. That second click is an easy drop-off point. It would be great if adding a connector could immediately kick off the OAuth authorization.

### Current flow

1. Open `…/customize/connectors?modal=add-custom-connector&connectorName=…&connectorUrl=…` → fields prefilled 🎉
2. Click **Add** → connector appears, **but not connected**
3. Click **Connect** → *now* the OAuth flow starts → Authorize

Steps 2 and 3 feel redundant when the server clearly supports OAuth.

### Request

When a connector is added and the server advertises OAuth (e.g. `WWW-Authenticate` / `.well-known/oauth-protected-resource` discovery), **start the authorization flow right after Add** instead of requiring a separate Connect click. Optionally gate it behind a deep-link param (e.g. `&connect=1`) for links that want the full one-shot flow.

### Why

- Fewer steps → higher completion, especially from install links / docs / directories.
- ChatGPT already initiates the connection immediately after you add a server — this would bring claude.ai to parity.
- Combined with #74, the whole flow becomes: **open link → Add → Authorize → done.**

Thanks!