feat: persistent storage for Deno static sites

- Add storage_enabled and storage_limit_mb columns to static_sites.
- Create/attach Docker volumes (tinyforge-site-{name}-data) for Deno
  sites with storage enabled, mounted at /app/data.
- Grant --allow-write=/app/data in Deno container CMD.
- Add storage usage API endpoint (GET /api/sites/{id}/storage).
- Show storage section in site detail page with usage bar.
- Add storage toggle and limit field to new site wizard.
- Use ConfirmDialog for secret deletion instead of inline delete.

internal/store/models.go

@@ -217,6 +217,8 @@ type StaticSite struct {
 	LastSyncAt     string `json:"last_sync_at"`
 	LastCommitSHA  string `json:"last_commit_sha"`
 	Error          string `json:"error"`
+	StorageEnabled bool   `json:"storage_enabled"`
+	StorageLimitMB int    `json:"storage_limit_mb"` // 0 = unlimited
 	CreatedAt      string `json:"created_at"`
 	UpdatedAt      string `json:"updated_at"`
 }