refactor(db): port metrics storage + service domains to sqlc (#75)

First tranche of the ~300-site raw SQL port. Metrics: node/service/
instance rows via generated queries; aggregation moved off TimescaleDB's
time_bucket onto portable date_bin (PG14+); interval uptime returns epoch
seconds; per-container writes dropped (container_metrics FKs a different
model — collector shape never matched). Domains: all reads/writes through
sqlcdb including the create transaction via WithTx; default-domain and
services.domain invariants unchanged. Both paths covered by live
Postgres tests gated on METRICS_TEST_DSN.

Generated with [Devin](https://devin.ai)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/sqlc/queries/domains.sql

@@ -0,0 +1,46 @@
+-- name: ListServiceDomains :many
+SELECT id, service_id, domain, is_default, cert_type, cert_status, last_checked_at, created_at
+FROM service_domains
+WHERE service_id = $1
+ORDER BY is_default DESC, created_at ASC;
+
+-- name: CountServiceDomains :one
+SELECT COUNT(*) FROM service_domains WHERE service_id = $1;
+
+-- name: ClearServiceDomainDefault :exec
+UPDATE service_domains SET is_default = false WHERE service_id = $1;
+
+-- name: CreateServiceDomain :one
+INSERT INTO service_domains (service_id, domain, is_default)
+VALUES ($1, $2, $3)
+RETURNING id, service_id, domain, is_default, cert_type, cert_status, created_at;
+
+-- name: DeleteServiceDomain :execrows
+DELETE FROM service_domains WHERE id = $1 AND service_id = $2;
+
+-- name: SetServiceDomainDefault :execrows
+UPDATE service_domains SET is_default = (id = $1) WHERE service_id = $2;
+
+-- name: TouchServiceDomainChecked :exec
+UPDATE service_domains SET last_checked_at = NOW() WHERE id = $1;
+
+-- name: GetServiceDomainDefault :one
+SELECT domain FROM service_domains WHERE service_id = $1 AND is_default;
+
+-- name: GetServiceDomainFirst :one
+SELECT domain FROM service_domains WHERE service_id = $1 ORDER BY created_at ASC LIMIT 1;
+
+-- name: SetServiceLegacyDomain :exec
+UPDATE services SET domain = $1 WHERE id = $2;
+
+-- name: GetServicePlacementBrief :one
+SELECT name, node_id, COALESCE(spread, false) AS spread FROM services WHERE id = $1;
+
+-- name: GetServiceAccess :one
+SELECT maintenance_mode, basic_auth_users FROM services WHERE id = $1;
+
+-- name: ServiceWriteAccess :one
+SELECT EXISTS(
+    SELECT 1 FROM services s JOIN projects p ON s.project_id = p.id
+    WHERE s.id = $1 AND (p.owner_id = $2 OR $3::bool)
+) AS allowed;