feat(worker,data): add git worktree support and conventional commits

GitService (in ClaudeDo.Data so the UI can reuse it) wraps the git CLI:
IsGitRepo, RevParseHead, WorktreeAdd/Remove, HasChanges, AddAll, Commit
(multi-line via -F -), DiffStat, BranchDelete, MergeFfOnly. Throws with
stderr on failure.

WorktreeManager owns the per-task lifecycle: validate working_dir is a
git repo (throws if not, no DB row written), create the worktree at
<repo>/../.claudedo-worktrees/<slug>/<id>/ (or central root per config),
insert the worktrees row. CommitIfChangedAsync skips when there are no
changes, otherwise commits and updates head_commit + diff_stat.

CommitMessageBuilder produces "{type}({list-slug}): {title<=60}" with a
blank-line-separated description (truncated to 400) and a permanent
"ClaudeDo-Task: <id>" trailer. Slug normalises whitespace + strips
non-alphanumerics. Newlines hard-coded to \n so git on Windows doesn't
choke on \r\n.

TaskRunner branches on list.WorkingDir: worktree path runs Claude in the
worktree, commits on success, broadcasts WorktreeUpdated; failure leaves
the worktree row active for inspection. Sandbox path unchanged.

Tests: 38 pass (12 new). GitRepoFixture spins up a real temp repo with a
seed commit; tests skip gracefully if `git` isn't on PATH.
CommitMessageBuilder fully unit-tested. WorktreeManager covers create,
no-change skip, real-commit, and non-repo failure.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/ClaudeDo.Worker.Tests/Infrastructure/GitRepoFixture.cs

@@ -0,0 +1,90 @@
+using System.Diagnostics;
+
+namespace ClaudeDo.Worker.Tests.Infrastructure;
+
+public sealed class GitRepoFixture : IDisposable
+{
+    public string RepoDir { get; }
+    public string BaseCommit { get; }
+
+    public GitRepoFixture()
+    {
+        RepoDir = Path.Combine(Path.GetTempPath(), $"claudedo_gittest_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(RepoDir);
+
+        RunGit(RepoDir, "init");
+        RunGit(RepoDir, "config", "user.name", "test");
+        RunGit(RepoDir, "config", "user.email", "test@example.com");
+
+        File.WriteAllText(Path.Combine(RepoDir, "README.md"), "# test repo");
+        RunGit(RepoDir, "add", "-A");
+        RunGit(RepoDir, "commit", "-m", "initial commit");
+
+        BaseCommit = RunGit(RepoDir, "rev-parse", "HEAD").Trim();
+    }
+
+    public void Dispose()
+    {
+        try
+        {
+            // Force-remove read-only .git objects on Windows.
+            ForceDeleteDirectory(RepoDir);
+        }
+        catch { /* best effort */ }
+    }
+
+    public static bool IsGitAvailable()
+    {
+        try
+        {
+            var psi = new ProcessStartInfo("git", "--version")
+            {
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
+                UseShellExecute = false,
+                CreateNoWindow = true,
+            };
+            using var p = Process.Start(psi)!;
+            p.WaitForExit(5000);
+            return p.ExitCode == 0;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
+    internal static string RunGit(string workDir, params string[] args)
+    {
+        var psi = new ProcessStartInfo("git")
+        {
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+            CreateNoWindow = true,
+        };
+        psi.ArgumentList.Add("-C");
+        psi.ArgumentList.Add(workDir);
+        foreach (var a in args) psi.ArgumentList.Add(a);
+
+        using var proc = Process.Start(psi)!;
+        var stdout = proc.StandardOutput.ReadToEnd();
+        var stderr = proc.StandardError.ReadToEnd();
+        proc.WaitForExit();
+
+        if (proc.ExitCode != 0)
+            throw new InvalidOperationException($"git {string.Join(' ', args)} failed: {stderr}");
+
+        return stdout;
+    }
+
+    private static void ForceDeleteDirectory(string path)
+    {
+        if (!Directory.Exists(path)) return;
+        foreach (var file in Directory.EnumerateFiles(path, "*", SearchOption.AllDirectories))
+        {
+            File.SetAttributes(file, FileAttributes.Normal);
+        }
+        Directory.Delete(path, true);
+    }
+}