feat(templates): remote template registry via CONTAINR_TEMPLATE_REGISTRY_URL

- GET /templates merges a remote Containr catalog as source:"registry"
  (5s timeout, 60s cache, offline-safe)
- GET /templates/:id falls through to the registry
- Deploy of a registry template materializes a deterministic private
  copy for the deployer — repeat deploys reuse it
- Templates page badges registry entries; openapi + env documented

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

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

app/backend/internal/api/templateregistry.go

@@ -0,0 +1,186 @@
+package api
+
+// Template registry — CONTAINR_TEMPLATE_REGISTRY_URL points at another
+// Containr instance (or any server answering the same template shape):
+//   GET {base}/api/v1/templates     → {"templates": [ServiceTemplate…]}
+//   GET {base}/api/v1/templates/:id → {"template": …, "config": …, "variables": …}
+// Registry entries merge into the catalog as source:"registry"; deploying
+// one materializes it as a user template for the deployer first. The
+// bundled catalog always works offline — a dead registry never blocks it.
+
+import (
+	"containr/internal/database/sqlcdb"
+	"context"
+	"crypto/sha256"
+	"database/sql"
+	"encoding/hex"
+	"encoding/json"
+	"net/http"
+	"os"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	"github.com/sqlc-dev/pqtype"
+)
+
+const registryCacheTTL = 60 * time.Second
+
+var registryCache struct {
+	mu        sync.Mutex
+	fetchedAt time.Time
+	templates []ServiceTemplate
+}
+
+func registryBaseURL() string {
+	base := strings.TrimRight(strings.TrimSpace(os.Getenv("CONTAINR_TEMPLATE_REGISTRY_URL")), "/")
+	base = strings.TrimSuffix(base, "/api/v1")
+	return base
+}
+
+// fetchRegistryTemplates lists the remote catalog, cached for
+// registryCacheTTL. Failures degrade to an empty list — never fatal.
+func fetchRegistryTemplates(ctx context.Context) []ServiceTemplate {
+	if registryBaseURL() == "" {
+		return nil
+	}
+	registryCache.mu.Lock()
+	fresh := time.Since(registryCache.fetchedAt) < registryCacheTTL && registryCache.templates != nil
+	cached := registryCache.templates
+	registryCache.mu.Unlock()
+	if fresh {
+		return cached
+	}
+
+	var templates []ServiceTemplate
+	var payload struct {
+		Templates []ServiceTemplate `json:"templates"`
+	}
+	if err := registryGet(ctx, "/api/v1/templates", &payload); err == nil {
+		templates = payload.Templates
+	}
+	for i := range templates {
+		templates[i].Source = "registry"
+	}
+
+	registryCache.mu.Lock()
+	registryCache.fetchedAt = time.Now()
+	registryCache.templates = templates
+	registryCache.mu.Unlock()
+	return templates
+}
+
+// fetchRegistryTemplate fetches one remote template's full document
+// (template + config + variables). nil when the registry lacks it.
+func fetchRegistryTemplate(ctx context.Context, id string) *ServiceTemplate {
+	base := registryBaseURL()
+	if base == "" {
+		return nil
+	}
+	var payload struct {
+		Template  ServiceTemplate    `json:"template"`
+		Config    json.RawMessage    `json:"config"`
+		Variables []TemplateVariable `json:"variables"`
+	}
+	if err := registryGet(ctx, "/api/v1/templates/"+id, &payload); err != nil {
+		return nil
+	}
+	t := payload.Template
+	if t.ID == "" {
+		t.ID = id
+	}
+	t.Source = "registry"
+	// The detail endpoint returns config/variables decoded; store them back
+	// as raw JSON so they can persist unmodified into a local copy.
+	if len(payload.Config) > 0 {
+		t.Config = string(payload.Config)
+	}
+	if payload.Variables != nil {
+		if raw, err := json.Marshal(payload.Variables); err == nil {
+			t.Variables = string(raw)
+		}
+	}
+	return &t
+}
+
+func registryGet(ctx context.Context, path string, out interface{}) error {
+	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, registryBaseURL()+path, nil)
+	if err != nil {
+		return err
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return errRegistry{resp.StatusCode}
+	}
+	return json.NewDecoder(resp.Body).Decode(out)
+}
+
+type errRegistry struct{ status int }
+
+func (e errRegistry) Error() string { return "template registry status " + http.StatusText(e.status) }
+
+// respondRegistryTemplate answers GET /templates/:id for a registry-only
+// template with the same envelope shape as local templates.
+func respondRegistryTemplate(c *gin.Context, t *ServiceTemplate) {
+	config := json.RawMessage(t.Config)
+	if len(config) == 0 {
+		config = json.RawMessage(`{}`)
+	}
+	variables := json.RawMessage(t.Variables)
+	if len(variables) == 0 {
+		variables = json.RawMessage(`[]`)
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"template":  t,
+		"config":    config,
+		"variables": variables,
+	})
+}
+
+// materializeRegistryTemplate copies a registry template into the local
+// catalog as a private template owned by the deployer, so the normal
+// deploy path (and future re-deploys) work without the registry. The
+// local id is deterministic per (registry, template, user) so repeat
+// deploys reuse the same copy instead of accumulating duplicates.
+func materializeRegistryTemplate(c *gin.Context, q *sqlcdb.Queries, userID, templateID string) (sqlcdb.ServiceTemplate, error) {
+	ownerUUID, err := uuid.Parse(userID)
+	if err != nil {
+		return sqlcdb.ServiceTemplate{}, err
+	}
+	sum := sha256.Sum256([]byte(registryBaseURL() + "|" + templateID + "|" + userID))
+	localID := "reg-" + hex.EncodeToString(sum[:8])
+	if existing, err := q.GetServiceTemplateByID(c.Request.Context(), localID); err == nil {
+		return existing, nil
+	}
+
+	rt := fetchRegistryTemplate(c.Request.Context(), templateID)
+	if rt == nil {
+		return sqlcdb.ServiceTemplate{}, sql.ErrNoRows
+	}
+	variables := pqtype.NullRawMessage{}
+	if rt.Variables != "" {
+		variables = pqtype.NullRawMessage{RawMessage: json.RawMessage(rt.Variables), Valid: true}
+	}
+	if err := q.CreateUserTemplate(c.Request.Context(), sqlcdb.CreateUserTemplateParams{
+		ID:          localID,
+		Name:        rt.Name,
+		Description: nullableText(rt.Description),
+		Category:    rt.Category,
+		Logo:        nullableText(rt.Logo),
+		Config:      json.RawMessage(rt.Config),
+		Variables:   variables,
+		OwnerID:     uuid.NullUUID{UUID: ownerUUID, Valid: true},
+		IsPublic:    false,
+	}); err != nil {
+		return sqlcdb.ServiceTemplate{}, err
+	}
+	return q.GetServiceTemplateByID(c.Request.Context(), localID)
+}