feat: durées en minutes + feedback visuel du retraitement

- Filtre format_duration : affiche les temps en min/s au lieu de secondes brutes
- Bouton reprocess : spinner animé, compteur temps réel, confirmation immédiate

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_viewer.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from src.viewer.app import create_app, compute_group_stats, severity_badge
+from src.viewer.app import create_app, compute_group_stats, severity_badge, format_duration
 from src.config import DossierMedical, Diagnostic, ActeCCAM
 
 
@@ -80,6 +80,23 @@ class TestSeverityBadgeFilter:
         assert result == ""
 
 
+class TestFormatDuration:
+    def test_none(self):
+        assert format_duration(None) == ""
+
+    def test_seconds_only(self):
+        assert format_duration(45.3) == "45.3s"
+
+    def test_minutes(self):
+        assert format_duration(150.0) == "2min 30s"
+
+    def test_exact_minutes(self):
+        assert format_duration(120.0) == "2min"
+
+    def test_large_duration(self):
+        assert format_duration(1257.65) == "20min 57s"
+
+
 class TestIndexPageLoads:
     def test_index_page_loads(self, client):
         response = client.get("/")