feat(api): Snapshot complete CRUD + enhanced SnapshotInfo

[AdaAibaby]

Problem

GET /snapshots lists snapshots but there is no way to retrieve a single snapshot by ID or delete one. The SnapshotInfo schema only exposes snapshotID and names — users cannot see resource specs (vCPU, RAM, disk) or creation time without listing all snapshots and filtering client-side.

Proposed changes

New endpoints

• GET /snapshots/{snapshotID} — return SnapshotInfo for a single snapshot (404 if not found or not owned by team)
• DELETE /snapshots/{snapshotID} — soft-delete a snapshot template, release its aliases, return 204

Enhanced SnapshotInfo

Add four fields populated from the existing ListTeamSnapshotTemplatesRow query result (no new DB queries needed):

Field	Source column
cpuCount	vcpu
memoryMB	ram_mb
diskSizeMB	total_disk_size_mb
createdAt	created_at

Implementation notes

• GET handler resolves the alias via templateCache.ResolveAlias (same path as POST /snapshots/{id}/fork) then calls ListTeamSnapshotTemplates with PageLimit=1.
• DELETE handler reuses the existing unexported softDeleteTemplate helper from template_delete.go and invalidates the template cache.
• api.gen.go is manually maintained (not regenerated from spec); updated by hand following existing patterns.