Certificate blocked: progress-check + Unit 7 assessment Spaces crash on the deleted `audio-course-u7-hands-on` dataset

### Summary
Learners cannot obtain the Audio Course certificate because **two maintainer-owned Spaces have been in `RUNTIME_ERROR` for ~6 weeks**, both tracing to the same deleted dataset:

- **`MariaK/Check-my-progress-Audio-Course`** (issues the completion/honors result) — still `RUNTIME_ERROR`
- **`huggingface-course/audio-course-u7-assessment`** (Unit 7 grader) — still `RUNTIME_ERROR`

Because the progress-check Space itself is down, even learners who have completed Units 4–6 cannot get their result — not just Honors.

### Root cause
Both Spaces depend on the dataset **`huggingface-course/audio-course-u7-hands-on`**, which now returns **404** (deleted or access-revoked).

1. **`Check-my-progress-Audio-Course`** — `app.py` calls `certification(hf_username)` at *import time* (line ~238, `value=certification(hf_username)`). That runs the Unit 7 `"demo"` branch, which does `hf_hub_download("huggingface-course/audio-course-u7-hands-on", "usernames.csv")`. Unlike every other branch, this one has **no `try/except`**, so the 404 raises during startup and the Space crashes.
2. **`audio-course-u7-assessment`** — a `Repository.git_pull()` of the same dataset 404s on boot (also surfaces as the misleading "No space left on device" symptom).

### Fix (one of)
- **Restore** the `huggingface-course/audio-course-u7-hands-on` dataset (or re-grant read access), **or**
- **Guard** the two downloads and stop calling `certification()` at import time in the progress-check Space (make the Unit 7 check degrade gracefully).

### Reproduction / evidence
- Space discussions with the diagnosis received no maintainer response: `Check-my-progress` #12 and `audio-course-u7-assessment` #23.
- A patched, working fork of the progress checker (guards the deleted-dataset download; Units 4–6 verified exactly as upstream): `VoicesColeby/audio-course-progress-check-fixed`.
- A patched fork of the Unit 7 assessor is also deployed: `VoicesColeby/audio-course-u7-assessment-fixed`.

Happy to open a PR against either Space if that's easier than restoring the dataset.

cc @MariaK

Start with app.py around line 238 and trace certification(hf_username), especially the Unit 7 demo branch and its hf_hub_download call. For the assessment Space, inspect the boot-time Repository.git_pull for the same dataset; discussions #12 and #23 contain evidence. Done means the Spaces no longer crash when the dataset returns 404, or the dataset is restored, with Units 4–6 still verified.

Written by the indexing model from the issue text.