v0.27.0 — user-configurable app subdomains

Users can now customize the subdomain for each app during deployment
instead of using a fixed value. The deploy page shows an editable text
input with the default pre-filled and the base domain as a suffix.

New "subdomain" deploy field type with DNS-safe format validation,
reserved name blocklist, and uniqueness check across deployed stacks.
Locked after deploy — changing requires Remove + Redeploy.

Backward compatible: InjectMissingFields() auto-fills SUBDOMAIN from
.felhom.yml defaults for existing deployed apps on next sync/restart.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/stacks/metadata.go

@@ -60,7 +60,7 @@ type ResourceHints struct {
 type DeployField struct {
 	EnvVar           string          `yaml:"env_var" json:"env_var"`
 	Label            string          `yaml:"label" json:"label"`
-	Type             string          `yaml:"type" json:"type"`               // domain, secret, password, path, text, select, boolean
+	Type             string          `yaml:"type" json:"type"`               // domain, subdomain, secret, password, path, text, select, boolean
 	Generate         string          `yaml:"generate" json:"generate"`       // e.g., "password:24", "hex:32", "static:admin"
 	Default          string          `yaml:"default" json:"default"`
 	Required         bool            `yaml:"required" json:"required"`
@@ -112,9 +112,9 @@ func LoadMetadata(stackDir string) Metadata {
 		meta.Category = "tools"
 	}
 
-	// DOMAIN field is always auto-filled — mark it implicitly required
+	// DOMAIN and SUBDOMAIN fields are always auto-filled/required — mark implicitly
 	for i := range meta.DeployFields {
-		if meta.DeployFields[i].Type == "domain" {
+		if meta.DeployFields[i].Type == "domain" || meta.DeployFields[i].Type == "subdomain" {
 			meta.DeployFields[i].Required = true
 			meta.DeployFields[i].LockedAfterDeploy = true
 		}