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.

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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.

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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.

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

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

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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.

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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/mcpserver/server.go

@@ -133,6 +133,7 @@ func init() {
 	register(spec{"containr_templates_deploy", "Deploy a template into a project. Args: id (template), project_id.", "POST", "/templates/{id}/deploy", []string{"id"}, []string{"project_id"}, false})
 	register(spec{"containr_templates_plan", "Dry-resolve a template: expanded expressions, service refs, missing variables. Args: id, variables (object).", "POST", "/templates/{id}/plan", []string{"id"}, nil, false})
 	register(spec{"containr_templates_import_compose", "Convert docker-compose YAML into a v2 template graph config. Args: compose_yaml.", "POST", "/templates/import/compose", nil, []string{"compose_yaml"}, false})
+	register(spec{"containr_templates_import_git", "Fetch a compose file from a git repo (clone URL, ssh remote, or owner/repo via connected providers) and convert it into a v2 template graph config. Args: repo (required), path (default: compose.yaml/yml or docker-compose.yml/yaml), ref (branch or commit).", "POST", "/templates/import/git", nil, []string{"repo", "path", "ref"}, false})
 	register(spec{"containr_templates_deploy_graph", "Deploy an ad-hoc service graph without a stored template. Args: project_id, config ({services:[...]}), variables, plan, region.", "POST", "/templates/deploy", nil, []string{"project_id", "config", "variables", "plan", "region"}, false})
 	register(spec{"containr_projects_import_compose", "Deploy a docker-compose file straight into a project. Args: id (project), compose_yaml, variables, plan, region.", "POST", "/projects/{id}/import-compose", []string{"id"}, []string{"compose_yaml", "variables", "plan", "region"}, false})