feat(monitoring/site-mappings): globalize site_domain_mappings

Drop tenant scoping on site_domain_mappings now that the citation query
resolves mappings without tenant filtering. Add a unique index on
registrable_domain plus an updated_at column, and switch the dev-seed
upsert to use ON CONFLICT (registrable_domain). Adds a SiteDomainMapping
type to ops/domain for the upcoming console management UI.

server/migrations_monitoring/20260429110000_globalize_site_domain_mappings.down.sql

@@ -0,0 +1,10 @@
+DROP INDEX IF EXISTS idx_site_domain_mappings_created;
+DROP INDEX IF EXISTS idx_site_domain_mappings_active_domain;
+DROP INDEX IF EXISTS uk_site_domain_mappings_domain;
+
+ALTER TABLE site_domain_mappings
+    ADD COLUMN IF NOT EXISTS tenant_id BIGINT,
+    DROP COLUMN IF EXISTS updated_at;
+
+CREATE INDEX IF NOT EXISTS idx_site_domain_mappings_lookup
+    ON site_domain_mappings(tenant_id, registrable_domain, is_active);