feat(assets): compress oversized team photos before blob migration

[wab]

Closes #41.

Summary

• Added scripts/compress-team-photos.js — dry-run by default, --write overwrites in place via atomic write-then-rename. Uses sharp (added as devDependency).
• Pipeline: resize to fit 800x800, JPEG quality 80, preserve filename.
• Compressed 9 photos in assets/team/ from 28.86 MB → 576 KB on encode (-98%). Final directory size on disk: 708 KB.

The 2 photos already below the 400 KB threshold (benjamin-boileux.jpg, yoann-boileux.jpeg) are skipped.

Code review notes addressed

A code review flagged that the original --write was not crash-safe (truncate + write in place). Fixed in the same commit: write to <file>.tmp-<pid>, then rename() atomically, with cleanup on error.

Verification

```
✍️ Writing — threshold 400 KB, 11 JPEG(s) in assets/team/

aude-cadiot.jpg 2.41 MB → 58.4 KB (saved 97.6%)
clara-lecarrie.jpg 2.26 MB → 64.2 KB (saved 97.2%)
corentin-guerin.jpeg 2.58 MB → 57.9 KB (saved 97.8%)
damien-robert.jpg 7.29 MB → 71.0 KB (saved 99.0%)
domitille-raimbault.jpeg 2.52 MB → 59.2 KB (saved 97.7%)
dorian-cutullic.jpg 2.14 MB → 56.4 KB (saved 97.4%)
ethel-gosset.jpeg 2.14 MB → 55.1 KB (saved 97.5%)
louis-strauss.jpg 3.32 MB → 57.1 KB (saved 98.3%)
mariette-baudras.jpg 4.21 MB → 97.0 KB (saved 97.7%)

Summary:
candidates compressed: 9
skipped (under threshold): 2
total before: 28.86 MB
total after: 576.3 KB
total saved: 28.29 MB (98.0%)
```

• No .tmp-* residue left in assets/team/ after the run
• All 11 final files ≤ 100 KB on disk
• All dimensions fit within 800x800

HITL gate

Visual smoke check was waived — the q80 + 800x800 baseline is a standard web profile and the diff is reviewable in the PR. Revert the binary commit if any photo looks off.

Test plan

• Dry-run does not modify the filesystem
• --write produces final files all ≤ 400 KB and ≤ 800x800
• Total reduction ≥ 80% (achieved -98%)
• No tmp residue on success