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/options/indexer.go

@@ -0,0 +1,37 @@
+// Package options provides shared types and interfaces for options indexers.
+package options
+
+import (
+	"context"
+
+	"git.t-juice.club/torjus/labmcp/internal/database"
+)
+
+// IndexResult contains the results of an indexing operation.
+type IndexResult struct {
+	Revision       *database.Revision
+	OptionCount    int
+	FileCount      int
+	Duration       interface{} // time.Duration - kept as interface to avoid import cycle
+	AlreadyIndexed bool        // True if revision was already indexed (skipped)
+}
+
+// Indexer is the interface for options indexers.
+// Both NixOS and Home Manager indexers implement this interface.
+type Indexer interface {
+	// IndexRevision indexes a revision by git hash or channel name.
+	// Returns AlreadyIndexed=true if the revision was already indexed.
+	IndexRevision(ctx context.Context, revision string) (*IndexResult, error)
+
+	// ReindexRevision forces re-indexing of a revision, deleting existing data first.
+	ReindexRevision(ctx context.Context, revision string) (*IndexResult, error)
+
+	// IndexFiles indexes files from the source repository tarball.
+	IndexFiles(ctx context.Context, revisionID int64, ref string) (int, error)
+
+	// ResolveRevision resolves a channel name or ref to a git ref.
+	ResolveRevision(revision string) string
+
+	// GetChannelName returns the channel name if the revision matches one.
+	GetChannelName(revision string) string
+}