feat(config): add git.author and git.no-gpg-sign options (fixes #600)

Adds configuration options for beads git commits:
- git.author: Override commit author (e.g., "beads-bot <beads@example.com>")
- git.no-gpg-sign: Disable GPG signing for beads commits

This is useful for users with Touch ID commit signing (like Secretive)
who get prompted for every beads auto-commit.

Config example:
```yaml
git:
  author: "beads-bot <beads@example.com>"
  no-gpg-sign: true
```

Environment variables: BD_GIT_AUTHOR, BD_GIT_NO_GPG_SIGN

Closes #600

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor/fix/untracked.go

@@ -6,6 +6,8 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+
+	"github.com/steveyegge/beads/internal/config"
 )
 
 // UntrackedJSONL stages and commits untracked .beads/*.jsonl files.
@@ -69,8 +71,21 @@ func UntrackedJSONL(path string) error {
 	}
 
 	// Commit only the JSONL files we staged (using --only to preserve other staged changes)
+	// Use config-based author and signing options (GH#600)
 	commitMsg := "chore(beads): commit untracked JSONL files\n\nAuto-committed by bd doctor --fix (bd-pbj)"
-	commitArgs := []string{"commit", "--only", "-m", commitMsg}
+	commitArgs := []string{"commit", "--only"}
+
+	// Add --author if configured
+	if author := config.GetString("git.author"); author != "" {
+		commitArgs = append(commitArgs, "--author", author)
+	}
+
+	// Add --no-gpg-sign if configured
+	if config.GetBool("git.no-gpg-sign") {
+		commitArgs = append(commitArgs, "--no-gpg-sign")
+	}
+
+	commitArgs = append(commitArgs, "-m", commitMsg)
 	commitArgs = append(commitArgs, untrackedFiles...)
 	commitCmd := exec.Command("git", commitArgs...) // #nosec G204 -- untrackedFiles validated above
 	commitCmd.Dir = path