docs: replace MinIO with filesystem storage throughout

Remove all MinIO/S3 references from documentation and deployment
configs. Silo now uses local filesystem storage exclusively.

Updated files:
- docs/CONFIGURATION.md: storage section now documents filesystem backend
- docs/DEPLOYMENT.md: architecture diagram, external services, troubleshooting
- docs/INSTALL.md: remove MinIO setup, update architecture diagrams
- docs/SPECIFICATION.md: architecture, technology stack, file storage strategy
- docs/STATUS.md: storage backend status
- docs/GAP_ANALYSIS.md: file handling references
- docs/ROADMAP.md: file storage appendix entries
- deployments/config.prod.yaml: filesystem backend config
- deployments/systemd/silod.env.example: remove MinIO credential vars

deployments/config.prod.yaml

@@ -10,8 +10,6 @@
 #
 # Credentials via environment variables (set in /etc/silo/silod.env):
 #   SILO_DB_PASSWORD
-#   SILO_MINIO_ACCESS_KEY
-#   SILO_MINIO_SECRET_KEY
 #   SILO_SESSION_SECRET
 #   SILO_ADMIN_PASSWORD
 
@@ -30,12 +28,9 @@ database:
   max_connections: 20
 
 storage:
-  endpoint: "minio.example.internal:9000"
-  access_key: "" # Set via SILO_MINIO_ACCESS_KEY
-  secret_key: "" # Set via SILO_MINIO_SECRET_KEY
-  bucket: "silo-files"
-  use_ssl: true
-  region: "us-east-1"
+  backend: "filesystem"
+  filesystem:
+    root_dir: "/opt/silo/data"
 
 schemas:
   directory: "/opt/silo/schemas"

deployments/systemd/silod.env.example

@@ -6,10 +6,6 @@
 # Database: silo, User: silo
 SILO_DB_PASSWORD=
 
-# MinIO credentials (minio.example.internal)
-# User: silouser
-SILO_MINIO_ACCESS_KEY=silouser
-SILO_MINIO_SECRET_KEY=
 
 # Authentication
 # Session secret (required when auth is enabled)