feat(templates): git compose import, six stack seeds, empty-default vars (#63)

* feat(templates): git compose import, six stack seeds, empty-default vars

- POST /templates/import/git fetches a compose file from any git remote
  (clone URL, ssh, owner/repo via connected providers — private repos
  included), ref selects branch or commit. Path defaults through
  compose.yaml/yml then docker-compose.yml/yaml. Reuses the build-on-node
  checkout machinery; repo-relative paths are containment-checked.
- CLI `templates import-git <repo> [path] [--ref]`, MCP
  containr_templates_import_git, OpenAPI entry, and a paste/git toggle
  in the template import dialog.
- {{VAR:-}} with an empty default now resolves instead of reporting the
  var missing — matches shell :- semantics.
- SeedTemplates gains six official graph stacks — n8n (pg+redis+worker),
  Gitea, Nextcloud, Vaultwarden, Umami, Immich — wired with
  {{service.*}} refs and {{secret}} credentials; no hardcoded passwords.
- TestSeedTemplatesResolveCleanly parses, topo-sorts, validates, and
  resolves every seeded graph — catalog drift can't merge silently.
- templates/n8n.md compose block had invalid YAML (mixed depends_on
  list/map) — fixed so the documented stack actually parses.

Verified live: import/git on a dumb-HTTP repo returns the converted
graph (db image → managed postgresql), path/ref/traversal/unauth edges
return clean errors, tpl-n8n plan resolves with zero unresolved vars.

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

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

* ci: pre-pull compose-smoke images via gcr mirror

Anonymous Docker Hub pulls rate-limit shared CI egress IPs — the compose
boot smoke flaked on traefik:pull. postgres/traefik are library/* images
served by mirror.gcr.io without auth; compose reuses the retagged local
images, falling back to a normal pull when the mirror misses.

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

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

* ci: route docker.io through gcr mirror for compose smoke

Pull-time pre-pulls don't cover BuildKit's base-image metadata lookups
(node:22-alpine, nginx:alpine, golang:1.26-alpine all 429). Daemon-level
registry-mirrors covers pulls and resolution in one move.

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

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

* ci: mirror docker.io in buildx for image publish job

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

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

* ci: route smoke pulls/builds through mirror.gcr.io via compose overlay

daemon.json registry-mirrors isn't honored by the runner's containerd
image store. Qualify refs directly: ARG-parameterized Dockerfile FROMs
(defaults unchanged) plus a CI-only compose overlay that points image
pulls and build args at mirror.gcr.io.

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

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

---------

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

app/backend/internal/api/templategraph.go

@@ -11,6 +11,8 @@ import (
 	"log"
 	"math/big"
 	"net/http"
+	"os"
+	"path/filepath"
 	"regexp"
 	"sort"
 	"strconv"
@@ -22,6 +24,7 @@ import (
 	"containr/internal/deployment"
 	"containr/internal/deployqueue"
 	"containr/internal/secrets"
+	"containr/internal/source"
 
 	"github.com/gin-gonic/gin"
 	"github.com/google/uuid"
@@ -227,7 +230,9 @@ func resolveStaticExpr(value string, userVars map[string]string, unresolved *[]s
 		if val, ok := userVars[key]; ok {
 			return val
 		}
-		if sub[2] != "" {
+		// {{VAR:-x}} supplies a default; {{VAR:-}} declares an explicitly
+		// empty one. Both resolve — only a bare {{VAR}} is unresolved.
+		if strings.Contains(m, ":-") {
 			return sub[2]
 		}
 		if unresolved != nil {
@@ -1112,6 +1117,130 @@ func handleImportCompose(c *gin.Context) {
 	})
 }
 
+// handleImportGitCompose fetches a compose file out of a git repository and
+// runs it through the same conversion as handleImportCompose. Works with any
+// git remote — connected providers (including GitHub App installs) supply
+// credentials for private repos. Nothing is persisted; the response feeds
+// the template create form or a direct deploy.
+func handleImportGitCompose(c *gin.Context) {
+	userID, ok := requireAuthenticatedUserID(c)
+	if !ok {
+		return
+	}
+	db := c.MustGet("db").(*database.DB)
+
+	var req struct {
+		Repo string `json:"repo" binding:"required"`
+		Path string `json:"path"`
+		Ref  string `json:"ref"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	branch, commit := "", ""
+	if ref := strings.TrimSpace(req.Ref); ref != "" {
+		if isCommitSHA(ref) {
+			commit = ref
+		} else {
+			branch = ref
+		}
+	}
+	spec, err := resolveGitCloneSpec(db, userID, req.Repo, branch, commit, "")
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error(), "code": "VALIDATION"})
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(c.Request.Context(), 2*time.Minute)
+	defer cancel()
+	checkoutRoot := filepath.Join(containrWorkDir, "repos", "import-"+uuid.NewString())
+	defer os.RemoveAll(checkoutRoot)
+	repoDir, err := source.Checkout(ctx, checkoutRoot, spec)
+	if err != nil {
+		c.JSON(http.StatusBadGateway, gin.H{"error": "git fetch failed: " + err.Error(), "code": "GIT_FETCH"})
+		return
+	}
+
+	// Default search order mirrors common compose conventions.
+	candidates := []string{req.Path}
+	if strings.TrimSpace(req.Path) == "" {
+		candidates = []string{"compose.yaml", "compose.yml", "docker-compose.yml", "docker-compose.yaml"}
+	}
+	var raw []byte
+	for _, rel := range candidates {
+		p, rerr := resolveRepoFile(repoDir, rel)
+		if rerr != nil {
+			continue
+		}
+		raw, err = os.ReadFile(p)
+		if err == nil {
+			break
+		}
+	}
+	if raw == nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "compose file not found in repository", "code": "NOT_FOUND"})
+		return
+	}
+	if len(raw) > 512*1024 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "Compose file exceeds 512 KiB"})
+		return
+	}
+
+	var file composeFileDef
+	if err := yaml.Unmarshal(raw, &file); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "Invalid compose YAML: " + err.Error()})
+		return
+	}
+	services, warnings, convErr := composeToSpecs(&file)
+	if convErr != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": convErr.Error()})
+		return
+	}
+	config := TemplateConfig{Version: 2, Services: services}
+	configJSON, _ := json.Marshal(config)
+	c.JSON(http.StatusOK, gin.H{
+		"config":    json.RawMessage(configJSON),
+		"variables": []TemplateVariable{},
+		"warnings":  warnings,
+	})
+}
+
+// resolveRepoFile maps a repo-relative file path onto the checkout and
+// rejects escapes — same containment rule as ResolveBuildPath, for files.
+func resolveRepoFile(checkoutDir, rel string) (string, error) {
+	rel = strings.TrimSpace(rel)
+	if rel == "" || filepath.IsAbs(rel) {
+		return "", fmt.Errorf("invalid repo path %q", rel)
+	}
+	clean := filepath.Clean(rel)
+	if clean == ".." || strings.HasPrefix(clean, ".."+string(filepath.Separator)) {
+		return "", fmt.Errorf("path escapes the checkout: %q", rel)
+	}
+	resolved := filepath.Join(checkoutDir, clean)
+	info, err := os.Stat(resolved)
+	if err != nil {
+		return "", fmt.Errorf("path %q not found in checkout", rel)
+	}
+	if !info.Mode().IsRegular() {
+		return "", fmt.Errorf("path %q is not a file", rel)
+	}
+	return resolved, nil
+}
+
+func isCommitSHA(ref string) bool {
+	if len(ref) != 40 {
+		return false
+	}
+	for _, r := range ref {
+		if !('0' <= r && r <= '9') && !('a' <= r && r <= 'f') {
+			return false
+		}
+	}
+	return true
+}
+
 // composeToSpecs converts a parsed compose file into graph service specs.
 // Compose service names become keys; declaration order follows YAML document
 // order — yaml.v3 maps lose order, so sort keys for stability.