feat: optional NPM proxy per stage

Add enable_proxy boolean to stages (default true). When disabled,
the deployer skips NPM proxy host creation — useful for internal
services, workers, or externally-routed containers. UI shows
toggle in Add Stage form and "No Proxy" badge on stage header.

internal/store/store.go

@@ -77,6 +77,8 @@ func (s *Store) runMigrations() error {
 		`ALTER TABLE registries ADD COLUMN owner TEXT NOT NULL DEFAULT ''`,
 		// Add base_volume_path to settings (2026-03-28).
 		`ALTER TABLE settings ADD COLUMN base_volume_path TEXT NOT NULL DEFAULT ''`,
+		// Add enable_proxy to stages (2026-03-29). Default true for backwards compat.
+		`ALTER TABLE stages ADD COLUMN enable_proxy INTEGER NOT NULL DEFAULT 1`,
 	}
 
 	for _, m := range migrations {
@@ -126,6 +128,7 @@ CREATE TABLE IF NOT EXISTS stages (
 	auto_deploy   INTEGER NOT NULL DEFAULT 0,
 	max_instances INTEGER NOT NULL DEFAULT 1,
 	confirm       INTEGER NOT NULL DEFAULT 0,
+	enable_proxy  INTEGER NOT NULL DEFAULT 1,
 	promote_from  TEXT NOT NULL DEFAULT '',
 	subdomain     TEXT NOT NULL DEFAULT '',
 	created_at    TEXT NOT NULL DEFAULT (datetime('now')),