feat: add hm-options package for Home Manager options

Add a new MCP server for Home Manager options, mirroring the
functionality of nixos-options but targeting the home-manager
repository.

Changes:
- Add shared options.Indexer interface for both implementations
- Add internal/homemanager package with indexer and channel aliases
- Add cmd/hm-options CLI entry point
- Parameterize MCP server with ServerConfig for name/instructions
- Parameterize nix/package.nix for building both packages
- Add hm-options package and NixOS module to flake.nix
- Add nix/hm-options-module.nix for systemd deployment

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

internal/nixos/indexer_test.go

@@ -99,7 +99,9 @@ func BenchmarkIndexRevision(b *testing.B) {
 		}
 
 		b.ReportMetric(float64(result.OptionCount), "options")
-		b.ReportMetric(float64(result.Duration.Milliseconds()), "ms")
+		if dur, ok := result.Duration.(time.Duration); ok {
+			b.ReportMetric(float64(dur.Milliseconds()), "ms")
+		}
 	}
 }
 
@@ -146,7 +148,9 @@ func BenchmarkIndexRevisionWithFiles(b *testing.B) {
 		fileDuration := time.Since(fileStart)
 
 		b.ReportMetric(float64(result.OptionCount), "options")
-		b.ReportMetric(float64(result.Duration.Milliseconds()), "options_ms")
+		if dur, ok := result.Duration.(time.Duration); ok {
+			b.ReportMetric(float64(dur.Milliseconds()), "options_ms")
+		}
 		b.ReportMetric(float64(fileCount), "files")
 		b.ReportMetric(float64(fileDuration.Milliseconds()), "files_ms")
 	}