feat: endpoint /health avec tests (8 tests)

Ajoute GET /health retournant un JSON avec :
- status: "ok"
- version: "2.1.0"
- ollama: true/false (connectivité testée avec timeout 2s)
- timestamp: ISO 8601 UTC

Tests couvrent : format JSON, champs requis, Ollama joignable/injoignable,
format timestamp ISO, type booléen du champ ollama.

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

src/viewer/app.py

@@ -616,4 +616,21 @@ def create_app() -> Flask:
                                metrics=metrics, total_selection=len(selection),
                                groups=groups)
 
+    # --- Health check endpoint ---
+    @app.route("/health")
+    def health():
+        from datetime import datetime, timezone
+        ollama_ok = False
+        try:
+            r = requests.get(f"{OLLAMA_URL}/api/tags", timeout=2)
+            ollama_ok = r.status_code == 200
+        except Exception:
+            pass
+        return jsonify({
+            "status": "ok",
+            "version": "2.1.0",
+            "ollama": ollama_ok,
+            "timestamp": datetime.now(timezone.utc).isoformat(),
+        })
+
     return app