feat: frame QC scoring + viser per-AUV button

Stage 04 frame extract:
- New lib_frame_qc.py: per-frame Laplacian/contrast/blue-dominance scoring
- Classes: bottom_visible / water_no_bottom / turbid_water / out_of_water
- Sample 1/5 frames after extraction, write qc.json per segment
- Record metrics (frames_total, frames_bottom_visible, bottom_visible_pct)
- Mark job degraded when bottom_visible_pct < 50%

Per-AUV viser view:
- scripts/viser_auv.py loads all PLYs of an AUV, color per file
- POST /pipeline/missions/{id}/auvs/{auv}/view rsyncs ply -> worker
- launches viser on hashed port 9300+, returns URL
- _pipeline.html exposes AUV list, JS handler opens viser tab

app/static/style.css

@@ -220,3 +220,12 @@ code { background: rgba(255,255,255,0.05); padding: 0 0.25rem; border-radius: 3p
 .status-degraded, .pj-badge.status-degraded { color: var(--warn); background: rgba(245,197,24,0.1); }
 .status-error, .pj-badge.status-error { color: var(--err); background: rgba(255,92,122,0.1); }
 .status-ingested, .pm-status.status-ingested { color: var(--accent); background: rgba(95,208,255,0.12); }
+
+/* AUV viser buttons (per-mission) */
+.pm-auvs { display: flex; gap: 0.4rem; flex-wrap: wrap; margin: 0.3rem 0 0.5rem; align-items: center; }
+.pm-auvs-label { color: var(--muted, #888); font-size: 0.72rem; text-transform: uppercase; letter-spacing: 0.05em; }
+.btn-viser-auv { font-size: 0.72rem; padding: 2px 8px; background: transparent;
+  border: 1px solid var(--accent, #4af); color: var(--accent, #4af); border-radius: 3px;
+  cursor: pointer; font-family: inherit; }
+.btn-viser-auv:hover { background: var(--accent, #4af); color: #062036; }
+.btn-viser-auv:disabled { opacity: 0.5; cursor: wait; }