feat: Archivum skeleton — Go/GraphQL backend + Vue 3 PWA frontend

Full project scaffold: multi-stage Dockerfile (ARM64/AMD64), AsciiDoc↔TipTap
bridge, Setup Wizard, CodeMirror source editor, Git-backed storage layer,
LDAP+JWT auth skeleton, Tailwind mobile-first layout, and VS Code build/push
tasks targeting registry at 192.168.0.19:5000.

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

backend/internal/git/git.go

@@ -0,0 +1,104 @@
+package git
+
+import (
+	"bytes"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+// Repo wraps a bare directory that is a Git repository.
+type Repo struct {
+	root string
+}
+
+// Open returns a Repo for an existing directory, initialising Git if needed.
+func Open(root string) (*Repo, error) {
+	r := &Repo{root: root}
+	if err := r.initIfNeeded(); err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+func (r *Repo) initIfNeeded() error {
+	out, _ := r.run("rev-parse", "--is-inside-work-tree")
+	if strings.TrimSpace(out) == "true" {
+		return nil
+	}
+	_, err := r.run("init")
+	return err
+}
+
+// Commit writes data to path and creates a Git commit authored by author.
+func (r *Repo) Commit(path, content, message, author, email string) error {
+	full := filepath.Join(r.root, path)
+	if err := writeFile(full, content); err != nil {
+		return err
+	}
+	if _, err := r.run("add", path); err != nil {
+		return err
+	}
+	_, err := r.run(
+		"-c", fmt.Sprintf("user.name=%s", author),
+		"-c", fmt.Sprintf("user.email=%s", email),
+		"commit", "-m", message,
+	)
+	return err
+}
+
+// Log returns the commit history for a file.
+func (r *Repo) Log(path string) ([]LogEntry, error) {
+	out, err := r.run("log", "--format=%H|%an|%ae|%ai|%s", "--", path)
+	if err != nil {
+		return nil, err
+	}
+	var entries []LogEntry
+	for _, line := range strings.Split(strings.TrimSpace(out), "\n") {
+		if line == "" {
+			continue
+		}
+		parts := strings.SplitN(line, "|", 5)
+		if len(parts) == 5 {
+			entries = append(entries, LogEntry{
+				Hash:    parts[0],
+				Author:  parts[1],
+				Email:   parts[2],
+				Date:    parts[3],
+				Subject: parts[4],
+			})
+		}
+	}
+	return entries, nil
+}
+
+// Diff returns the unified diff between two commits for a file.
+func (r *Repo) Diff(path, fromHash, toHash string) (string, error) {
+	out, err := r.run("diff", fromHash, toHash, "--", path)
+	return out, err
+}
+
+// Show returns the file content at a specific commit.
+func (r *Repo) Show(hash, path string) (string, error) {
+	return r.run("show", fmt.Sprintf("%s:%s", hash, path))
+}
+
+type LogEntry struct {
+	Hash    string
+	Author  string
+	Email   string
+	Date    string
+	Subject string
+}
+
+func (r *Repo) run(args ...string) (string, error) {
+	cmd := exec.Command("git", append([]string{"-C", r.root}, args...)...)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return "", fmt.Errorf("git %v: %w — %s", args, err, stderr.String())
+	}
+	return stdout.String(), nil
+}