U3: swap storage.*/snapshot.* to v1 endpoints (follow-up to backend #99)

[pparage]

Problem

Follow-up to backend PR #99 (range42-backend-api). The new v1 Proxmox storage and per-VM snapshot endpoints exist, but the UI still calls the v0 equivalents.

Backend v1 endpoints now available

• GET /v1/proxmox/hosts/{id}/storage
• GET /v1/proxmox/hosts/{id}/storage/{store}/content?content=iso|vztmpl
• POST /v1/proxmox/hosts/{id}/storage/{store}/download-url
• GET/POST/DELETE /v1/proxmox/hosts/{id}/vms/{vmid}/snapshots[...]/rollback

Work (src/services/proxmox/api.ts)

• storage.* (list/listIsos/listTemplates/downloadIso) → repoint to the v1 paths above; .items-unwrap the Page (mirror listHostVms); drop the proxmox_node arg (resolve host via getRegisteredHost()). Update useProxmoxStorage.ts + TemplateBrowser.vue.
• snapshot.* (create/list/revert/delete) → repoint to the per-VM v1 snapshot endpoints. Note: the current per-VM snapshot UI is wired to deployment-scoped /v1/deployments/:id/snapshot, and runnerCalls/snapshots/* use an Ansible bundle path — decide which consumers move.
• Add a per-VM snapshot section in ConfigPanel if per-node snapshot UX is wanted (currently none consumes the v1 per-VM endpoints).

Notes

• Response shapes: StorageContent includes a derived name (PVE doesn't return it); pools expose storage/type/content/active.
• Resolves the storage setConfig refactor surface (see the TemplateBrowser runtime-error issue).