feat: build-on-node — git checkouts, remote image builds, image transport (#60)

Git-sourced deploys never materialized a checkout: sourcePath was
build_path resolved against the server cwd, so builds consumed the
backend's own directory. Remote placement could only run
registry-pulled images.

- internal/source: per-deployment checkout (init/fetch/checkout) at
  branch or commit; GIT_ASKPASS keeps tokens out of argv, .git/config,
  and the build context; dumb-transport and SHA-refusal fallbacks;
  build_path validated inside the checkout.
- BuildManager.PackageContext: produces the same tar context Build
  ships to the daemon — generated Dockerfile at tar root, .git
  excluded. Fixes nixpacks passing the Dockerfile path as content.
- Agent artifact endpoint: GET /api/agents/artifacts/:id streams
  build contexts and docker-save tarballs behind agent-token auth;
  hex-validated ids, per-deployment cleanup, boot-time purge.
- Agent commands: build_image (docker build -, --build-arg values via
  process env, not argv) and load_image (docker load for containr-*
  rollback tags no registry serves).
- Deployment flow: remote git builds package context → artifact →
  node docker-builds the deployment tag; remote rollbacks of local
  tags export via SaveImage → artifact → node docker-loads.

Verified end-to-end: agent-pinned git service built on the node
(build_image → create_container → deployed) and rollback shipped a
docker-save tarball (load_image → deployed). Artifact auth returns
401/404 correctly; workspaces and blobs are removed after deploy.

Authored By: TDvorak <[email protected]>

app/backend/internal/api/gitcreds.go

@@ -0,0 +1,84 @@
+package api
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"containr/internal/database"
+	"containr/internal/source"
+)
+
+// resolveGitCloneSpec turns a service's git_repo (clone URL, ssh remote, or
+// owner/repo) into a source.Spec with the project owner's provider token.
+// Public repos get no token — the clone proceeds anonymously. github_app
+// providers store the installation id, not a usable token; a fresh
+// installation token is minted per deploy.
+func resolveGitCloneSpec(db *database.DB, ownerID, gitRepo, branch, commit, buildPath string) (source.Spec, error) {
+	raw := strings.TrimSpace(gitRepo)
+	cloneURL, err := source.NormalizeCloneURL(raw)
+	if err != nil {
+		return source.Spec{}, err
+	}
+
+	spec := source.Spec{Branch: branch, Commit: commit, BuildPath: buildPath}
+
+	var providerID string
+	if !strings.Contains(cloneURL, "://") {
+		// Bare owner/repo — the connected repository row knows the host.
+		err = db.QueryRow(
+			`SELECT clone_url, provider_id FROM git_repositories
+			 WHERE full_name = $1 AND user_id = $2 LIMIT 1`,
+			cloneURL, ownerID,
+		).Scan(&cloneURL, &providerID)
+		if err != nil {
+			return source.Spec{}, fmt.Errorf("repository %s is not connected — connect it under Git settings or store a clone URL", raw)
+		}
+	} else {
+		// URL form — match a connected repo for its provider when possible;
+		// an unmatched public URL still clones, just without credentials.
+		_ = db.QueryRow(
+			`SELECT provider_id FROM git_repositories
+			 WHERE clone_url = $1 AND user_id = $2 LIMIT 1`,
+			cloneURL, ownerID,
+		).Scan(&providerID)
+	}
+
+	if err := source.ValidateRemoteURL(cloneURL); err != nil {
+		return source.Spec{}, err
+	}
+	spec.CloneURL = cloneURL
+
+	if providerID == "" {
+		return spec, nil
+	}
+	var name, apiURL, token string
+	if err := db.QueryRow(
+		`SELECT name, api_url, access_token FROM git_providers
+		 WHERE id = $1 AND user_id = $2`,
+		providerID, ownerID,
+	).Scan(&name, &apiURL, &token); err != nil {
+		return spec, nil // provider row gone — anonymous clone still works for public repos
+	}
+
+	switch strings.ToLower(name) {
+	case "github_app":
+		installationID, err := strconv.ParseInt(strings.TrimSpace(token), 10, 64)
+		if err == nil && installationID > 0 {
+			if minted, err := getGitHubAppInstallationToken(apiURL, installationID); err == nil {
+				spec.Token = minted
+				spec.User = "x-access-token"
+			}
+		}
+	case "gitlab":
+		spec.Token = token
+		spec.User = "oauth2"
+	case "bitbucket":
+		spec.Token = token
+		spec.User = "x-token-auth"
+	default:
+		spec.Token = token
+		spec.User = "x-access-token"
+	}
+	return spec, nil
+}