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

docs/ROADMAP.md

@@ -313,7 +313,7 @@ For full SOLIDWORKS PDM comparison tables, see [GAP_ANALYSIS.md Appendix C](GAP_
 - Rollback functionality
 
 #### File Management
-- MinIO integration with versioning
+- Filesystem-based file storage
 - File upload/download via REST API
 - SHA256 checksums for integrity
 - Storage path: `items/{partNumber}/rev{N}.FCStd`
@@ -377,8 +377,8 @@ For full SOLIDWORKS PDM comparison tables, see [GAP_ANALYSIS.md Appendix C](GAP_
 
 ## Appendix B: Phase 1 Detailed Tasks
 
-### 1.1 MinIO Integration -- COMPLETE
-- [x] MinIO service configured in Docker Compose
+### 1.1 File Storage -- COMPLETE
+- [x] Filesystem storage backend
 - [x] File upload via REST API
 - [x] File download via REST API (latest and by revision)
 - [x] SHA256 checksums on upload