feat: support claude.local.md for local-only documentation

Add support for claude.local.md and .claude/claude.local.md as local-only
alternatives to CLAUDE.md. These files are intended to be gitignored for
personal customizations that should not be committed to the repo.

Changes:
- Update CheckAgentDocumentation to detect claude.local.md files
- Update CheckLegacyBeadsSlashCommands to check claude.local.md files
- Update CheckDocumentationBdPrimeReference to check claude.local.md files
- Add fix message mentioning claude.local.md as an option
- Add test cases for claude.local.md support

Closes #488

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

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

cmd/bd/doctor/claude.go

@@ -296,11 +296,15 @@ func CheckBdInPath() DoctorCheck {
 // CheckDocumentationBdPrimeReference checks if AGENTS.md or CLAUDE.md reference 'bd prime'
 // and verifies the command exists. This helps catch version mismatches where docs
 // reference features not available in the installed version.
+// Also supports local-only variants (claude.local.md) that are gitignored.
 func CheckDocumentationBdPrimeReference(repoPath string) DoctorCheck {
 	docFiles := []string{
 		filepath.Join(repoPath, "AGENTS.md"),
 		filepath.Join(repoPath, "CLAUDE.md"),
 		filepath.Join(repoPath, ".claude", "CLAUDE.md"),
+		// Local-only variants (not committed to repo)
+		filepath.Join(repoPath, "claude.local.md"),
+		filepath.Join(repoPath, ".claude", "claude.local.md"),
 	}
 
 	var filesWithBdPrime []string