fix(frontend): agent credentials improvements (#11763)

## Changes 🏗️

### System credentials in Run Modal

We had the issue that "system" credentials were mixed with "user"
credentials in the run agent modal:

#### Before

<img width="400" height="466" alt="Screenshot 2026-01-14 at 19 05 56"
src="https://github.com/user-attachments/assets/9d1ee766-5004-491f-ae14-a0cf89a9118e"
/>

This created confusion among the users. This "system" credentials are
supplied by AutoGPT ( _most of the time_ ) and a user running an agent
should not bother with them ( _unless they want to change them_ ). For
example in this case, the credential that matters is the **Google** one
🙇🏽

### After

<img width="400" height="350" alt="Screenshot 2026-01-14 at 19 04 12"
src="https://github.com/user-attachments/assets/e2bbc015-ce4c-496c-a76f-293c01a11c6f"
/>

<img width="400" height="672" alt="Screenshot 2026-01-14 at 19 04 19"
src="https://github.com/user-attachments/assets/d704dae2-ecb2-4306-bd04-3d812fed4401"
/>

"System" credentials are collapsed by default, reducing noise in the
Task Credentials section. The user can still see and change them by
expanding the accordion.

<img width="400" height="190" alt="Screenshot 2026-01-14 at 19 04 27"
src="https://github.com/user-attachments/assets/edc69612-4588-48e4-981a-f59c26cfa390"
/>

If some "system" credentials are missing, there is a red label
indicating so, it wasn't that obvious with the previous implementation,

<img width="400" height="309" alt="Screenshot 2026-01-14 at 19 04 30"
src="https://github.com/user-attachments/assets/f27081c7-40ad-4757-97b3-f29636616fc2"
/>

### New endpoint

There is a new REST endpoint, `GET /providers/system`, to list system
credential providers so it is easy to access in the Front-end to group
them together vs user ones.

### Other improvements

#### `<CredentialsInput />` refinements

<img width="715" height="200" alt="Screenshot 2026-01-14 at 19 09 31"
src="https://github.com/user-attachments/assets/01b39b16-25f3-428d-a6c8-da608038a38b"
/>

Use a normal browser `<select>` for the Credentials Dropdown ( _when you
have more than 1 for a provider_ ). This simplifies the UI shennagians a
lot and provides a better UX in 📱 ( _eventually we should move all our
selects to the native ones as they are much better for mobile and touch
screens and less code to maintain our end_ ).

I also renamed some files for clarity and tidied up some of the existing
logic.

#### Other

- Fix **Open telemetry** warnings on the server console by making the
packages external
- Fix `require-in-the-middle` console warnings
- Prettier tidy ups

## Checklist 📋

### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] Run the app locally and test the above