feat(nodes): per-node default domain with auto service hostnames (#65)

node_agents.default_domain gives each agent a base domain. Services
placed on it (explicit pin or spread) with no explicit service_domains
get <name>.<default_domain> — resolved in serviceDomainNames so edge
routing, wake placeholders, and public_url all see the same names.
Spread services union every eligible node's base domain; explicit
domains always win.

Surfaces: PUT /agents/:id {default_domain} (hostname-validated), CLI
nodes update --domain, MCP arg docs, OpenAPI + regenerated types,
node-detail inline editor.

Also marks the already-shipped backup-import roadmap item.

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

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

app/backend/internal/database/sqlcdb/models.go

@@ -178,6 +178,7 @@ type NodeAgent struct {
 	AutoPrune     bool                  `json:"auto_prune"`
 	Schedulable   bool                  `json:"schedulable"`
 	Tags          json.RawMessage       `json:"tags"`
+	DefaultDomain string                `json:"default_domain"`
 }
 
 type Notification struct {
@@ -279,6 +280,7 @@ type Service struct {
 	NodeID          sql.NullString  `json:"node_id"`
 	Spread          bool            `json:"spread"`
 	PlacementTags   json.RawMessage `json:"placement_tags"`
+	TraefikLabels   json.RawMessage `json:"traefik_labels"`
 }
 
 type ServiceDomain struct {