feat: implement database and storage abstractions

- Added `internal/db/store.go` to define the Store interface for database operations, including user, organization, app, channel, release, patch, and artifact management.
- Introduced `internal/models/models.go` changes to reflect updated organization and artifact response structures.
- Created `internal/storage/factory.go`, `local.go`, and `s3.go` to implement storage backends for local filesystem and S3-compatible services.
- Removed deprecated `internal/storage/storage.go` and refactored storage interface into `internal/storage/store.go`.
- Updated frontend JavaScript in `web/js/app.js` to display server health information, including storage and database backend details.

.env.example

@@ -1,23 +1,36 @@
 # Shorebird Self-Hosted Server Configuration
-# Copy this file to .env and adjust values as needed
+# Copy this file to .env and adjust values as needed.
 
-# Server
+# --- Server ---
 SERVER_HOST=0.0.0.0
 SERVER_PORT=8080
+# Public-facing URL (used for download links in local storage mode)
+SERVER_BASE_URL=http://localhost:8080
 
-# PostgreSQL Database
-DATABASE_URL=postgres://shorebird:shorebird@localhost:5432/shorebird?sslmode=disable
+# --- Database ---
+# Driver: "sqlite" (default, zero-dependency) or "postgres"
+DB_DRIVER=sqlite
+# SQLite path (relative to working directory; data/ is auto-created)
+DB_PATH=data/shorebird.db
+# PostgreSQL URL (only used when DB_DRIVER=postgres)
+# DATABASE_URL=postgres://shorebird:shorebird@localhost:5432/shorebird?sslmode=disable
 
-# Object Storage (MinIO / S3-compatible)
-STORAGE_ENDPOINT=localhost:9000
-STORAGE_ACCESS_KEY=minioadmin
-STORAGE_SECRET_KEY=minioadmin
-STORAGE_RELEASE_BUCKET=shorebird-releases
-STORAGE_PATCH_BUCKET=shorebird-patches
+# --- Storage ---
+# Driver: "local" (default, zero-dependency) or "s3"
+STORAGE_DRIVER=local
+# Local storage directory (auto-created)
+STORAGE_LOCAL_DIR=data/storage
+# S3/MinIO settings (only used when STORAGE_DRIVER=s3)
+# STORAGE_S3_ENDPOINT=localhost:9000
+# STORAGE_S3_ACCESS_KEY=minioadmin
+# STORAGE_S3_SECRET_KEY=minioadmin
+# STORAGE_S3_USE_SSL=false
+# STORAGE_S3_RELEASE_BUCKET=shorebird-releases
+# STORAGE_S3_PATCH_BUCKET=shorebird-patches
 
-# JWT Authentication
+# --- Authentication ---
 JWT_SECRET=change-me-in-production-use-a-long-random-string
 
-# Redis (optional, for caching patch checks)
-REDIS_ADDR=localhost:6379
-REDIS_PASSWORD=
+# --- Redis (optional) ---
+# REDIS_ADDR=localhost:6379
+# REDIS_PASSWORD=