feat(aws): SNS in Cloud Explorer

[hectorvent]

Add SNS to the Cloud Explorer (aws)

The aws emulator implements SNS (~27 operations). The UI does not surface it yet.

Backend (packages/api)

• src/cloud-spi/snsSchema.ts — snsSchemaFor('aws') (model: src/cloud-spi/storageSchema.ts)
• src/adapter-aws/AwsSnsAdapter.ts implements CloudServiceAdapter + AwsSnsAdapter.test.ts (model: src/adapter-aws/AwsStorageAdapter.ts)
• Register new AwsSnsAdapter() in src/cloudProxy.ts; add services.push({...}) + schema() fallback in src/service/CloudProxyService.ts

Frontend (packages/frontend)

• Verify nav shows SNS for aws and normalizeService() handles the literal (pages/CloudExplorerPage.tsx)
• Confirm generic DynamicResourceView rendering; add a service === '...' panel only if deep UX is needed

Acceptance

• SNS appears in the aws nav; list / create / delete / inspect work against the local emulator
• Adapter unit test passes

Depends on #66 (new messaging service type).
Emulator source: floci/src/main/java/io/github/hectorvent/floci/services/sns/