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.

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

app/backend/sqlc/queries/agents.sql

@@ -179,6 +179,18 @@ LIMIT 1;
 -- name: SetAgentTags :exec
 UPDATE node_agents SET tags = $2::jsonb, updated_at = NOW() WHERE id = $1;
 
+-- name: SetAgentDefaultDomain :exec
+UPDATE node_agents SET default_domain = $2, updated_at = NOW() WHERE id = $1;
+
+-- name: ListSchedulableAgentDomains :many
+-- Base domains of every online, schedulable agent carrying the required
+-- placement tags — auto-domain candidates for spread services.
+SELECT DISTINCT default_domain FROM node_agents
+WHERE status = 'online' AND schedulable
+  AND default_domain <> ''
+  AND tags @> $1::jsonb
+ORDER BY default_domain;
+
 -- name: ListServiceContainers :many
 SELECT id, name, node_agent_id, status, ports, resources FROM container_instances
 WHERE service_id = $1;