Allow campaign conversion goals to be marked as non-biddable

We need to update our campaign conversion goals so that **completed purchases are the only biddable event**.

The MCP lets us read the current campaign goal settings, but it doesn’t appear to expose a write operation for changing whether a campaign conversion goal is biddable. Because of this, we cannot configure the campaigns as follows:

| Category | Origin | Biddable |
|---|---|---:|
| `PURCHASE` | `WEBSITE` | `true` |
| `ADD_TO_CART` | `WEBSITE` | `false` |
| `BEGIN_CHECKOUT` | `WEBSITE` | `false` |
| `PAGE_VIEW` | `WEBSITE` | `false` |
| `DOWNLOAD` | `APP` | `false` |

We still want add-to-cart, begin-checkout, page-view, and app-download events available as secondary/diagnostic conversions. We just don’t want the campaigns bidding or optimizing toward them.

Would it be possible to expose a write operation for updating campaign conversion-goal biddability, using the MCP’s existing preview, dry-run, confirmation, and verification workflow?

I'm currently out on vacation but our Hermes agent flagged some poor optimization practices in the campaign. Unfortunately, we weren't able to address them asynchronously because the MCP doesn't expose the necessary functionality. If not addressed by the time I'm back, I can tackle it myself if you're planning on actively maintaining the repository.

Thank you!