feat: refresh a single account from its card

[caigee-cmd]

Summary

• Accounts had no per-account refresh: the only way to update one card was "Refresh credits", which re-probed every account in the pool.
• Adds POST /api/accounts/{id}/refresh, which re-probes one account's health, quota, and model catalog and returns just that account's view.
• The card swaps to a skeleton while the refresh runs, so stale quota and status are never left on screen (matching how the list behaves on a full refresh).
• The page then re-reads the pool so header counts and provider tallies stay in sync with the refreshed card.
• The route dispatches before the provider-native action block, which would otherwise reject refresh as an unknown action for non-Qoder providers.

Test plan

• go test ./...
• go vet ./...
• cd worker && npm test
• cd frontend && npm run build && npm run lint (0 errors; 14 warnings are pre-existing in untouched files)
• No tokens, auth blobs, raw captures, or host details in the diff

Notes

• internal/accounts saw one flaky failure during a full go test ./... run: sql: database is closed from the background cooldown-persistence goroutine at shutdown, not an assertion failure. It did not reproduce in 14 consecutive runs (including 6 on a clean tree without these changes), so it looks pre-existing and unrelated, but flagging it rather than hiding it.