fix(deploy): use /ready/ healthcheck and /srv/mnemosyne path

- Change app healthcheck from /live/ to /ready/ to verify full
  readiness including dependencies (DB, Neo4j, S3)
- Increase healthcheck timeout from 5s to 10s to accommodate
  dependency checks
- Add S3 bucket connectivity check to readiness probe
- Update deployment documentation to use /srv/mnemosyne instead
  of /opt/mnemosyne as the compose project directory

mnemosyne/mnemosyne/views.py

@@ -52,6 +52,30 @@ def live(request):
     return JsonResponse({"status": "ok"})
 
 
+def _check_s3() -> str | None:
+    """Return an error string if the Mnemosyne S3 bucket is unreachable, else None."""
+    import boto3
+    import botocore.exceptions
+    from django.conf import settings
+
+    try:
+        client = boto3.client(
+            "s3",
+            endpoint_url=settings.AWS_S3_ENDPOINT_URL or None,
+            aws_access_key_id=settings.AWS_ACCESS_KEY_ID or None,
+            aws_secret_access_key=settings.AWS_SECRET_ACCESS_KEY or None,
+            region_name=settings.AWS_S3_REGION_NAME or None,
+            use_ssl=getattr(settings, "AWS_S3_USE_SSL", True),
+            verify=getattr(settings, "AWS_S3_VERIFY", True),
+        )
+        client.head_bucket(Bucket=settings.AWS_STORAGE_BUCKET_NAME)
+        return None
+    except botocore.exceptions.ClientError as e:
+        return f"HTTP {e.response['Error']['Code']}"
+    except Exception as e:
+        return str(e)
+
+
 def ready(request):
     errors = {}
     try:
@@ -62,6 +86,9 @@ def ready(request):
         cache.get("__readiness_probe__")
     except Exception as e:
         errors["cache"] = str(e)
+    s3_error = _check_s3()
+    if s3_error:
+        errors["s3"] = s3_error
     if errors:
         return JsonResponse({"status": "error", "errors": errors}, status=503)
     return JsonResponse({"status": "ok"})