feat: volume scopes redesign — replace shared/isolated with 6 scopes

Replace confusing shared/isolated volume modes with explicit scopes:
- instance: per-deploy isolated directory
- stage: shared within a stage across deploys
- project: shared across all stages
- project_named: named group within a project
- named: global named volume across projects
- ephemeral: tmpfs in-memory mount

Includes schema migration (shared→project, isolated→instance),
backward-compatible deployer resolution, scope metadata API endpoint,
and redesigned volume editor UI with scope guide cards and hints.

web/src/lib/api.ts

@@ -20,7 +20,8 @@ import type {
 	StageEnv,
 	StandaloneProxy,
 	ValidationResult,
-	Volume
+	Volume,
+	VolumeScopeInfo
 } from './types';
 
 // ── Helpers ─────────────────────────────────────────────────────────
@@ -327,7 +328,7 @@ export function listVolumes(projectId: string): Promise<Volume[]> {
 
 export function createVolume(
 	projectId: string,
-	data: { source: string; target: string; mode?: string }
+	data: { source: string; target: string; scope: string; name?: string; mode?: string }
 ): Promise<Volume> {
 	return post<Volume>(`/api/projects/${projectId}/volumes`, data);
 }
@@ -335,11 +336,15 @@ export function createVolume(
 export function updateVolume(
 	projectId: string,
 	volId: string,
-	data: { source?: string; target?: string; mode?: string }
+	data: { source?: string; target?: string; scope?: string; name?: string; mode?: string }
 ): Promise<Volume> {
 	return put<Volume>(`/api/projects/${projectId}/volumes/${volId}`, data);
 }
 
+export function listVolumeScopes(): Promise<VolumeScopeInfo[]> {
+	return get<VolumeScopeInfo[]>('/api/volumes/scopes');
+}
+
 export function deleteVolume(
 	projectId: string,
 	volId: string