refactor: remove unused bd pin/unpin/hook commands (bd-x0zl)

Analysis found these commands are dead code:
- gt never calls `bd pin` - uses `bd update --status=pinned` instead
- Beads.Pin() wrapper exists but is never called
- bd hook functionality duplicated by gt mol status
- Code comment says "pinned field is cosmetic for bd hook visibility"

Removed:
- cmd/bd/pin.go
- cmd/bd/unpin.go
- cmd/bd/hook.go

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

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

cmd/bd/doctor/git_test.go

@@ -23,8 +23,8 @@ func setupGitRepo(t *testing.T) string {
 		t.Fatalf("failed to create .beads directory: %v", err)
 	}
 
-	// Initialize git repo
-	cmd := exec.Command("git", "init")
+	// Initialize git repo with 'main' as default branch (modern git convention)
+	cmd := exec.Command("git", "init", "--initial-branch=main")
 	cmd.Dir = dir
 	if err := cmd.Run(); err != nil {
 		t.Fatalf("failed to init git repo: %v", err)
@@ -278,8 +278,8 @@ func setupGitRepoInDir(t *testing.T, dir string) {
 		t.Fatalf("failed to create .beads directory: %v", err)
 	}
 
-	// Initialize git repo
-	cmd := exec.Command("git", "init")
+	// Initialize git repo with 'main' as default branch (modern git convention)
+	cmd := exec.Command("git", "init", "--initial-branch=main")
 	cmd.Dir = dir
 	if err := cmd.Run(); err != nil {
 		t.Fatalf("failed to init git repo: %v", err)