chore: add CLAUDE.md and gitignore

- Add project context file for Claude
- Ignore nix result symlink

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

CLAUDE.md

@@ -78,18 +78,32 @@ The first MCP server provides search and query capabilities for NixOS configurat
 - Support friendly aliases: `nixos-unstable`, `nixos-24.05`, `nixos-23.11`, etc.
 - Can be used in place of git hashes in all tools
 
-## Database Schema (Planned)
+## Database Schema
 
 **Tables:**
-- `revisions` - nixpkgs git hash, date, channel name, metadata
-- `options` - per revision: name, type, default, example, description
-- `declarations` - file paths where options are declared
-- `files` - cached nixpkgs file contents for `get_file` tool
+
+1. `revisions` - Indexed nixpkgs versions
+   - id, git_hash (unique), channel_name, commit_date, indexed_at, option_count
+
+2. `options` - NixOS options with hierarchy support
+   - id, revision_id (FK), name, parent_path, type, default_value (JSON text), example (JSON text), description, read_only
+   - parent_path enables efficient "list children" queries (derived from name)
+
+3. `declarations` - File paths where options are declared
+   - id, option_id (FK), file_path, line_number
+
+4. `files` - Cached file contents
+   - id, revision_id (FK), file_path, extension, content
+   - Configurable whitelist of extensions (default: .nix, .json, .md, .txt, .toml, .yaml, .yml)
 
 **Indexes:**
-- Full-text search on option names and descriptions
-- B-tree indexes on revision + option name
-- Namespace prefix indexes for category filtering
+- Full-text search: PostgreSQL (tsvector/GIN), SQLite (FTS5)
+- B-tree on (revision_id, name) and (revision_id, parent_path)
+- B-tree on (revision_id, file_path) for file lookups
+
+**Cross-DB Compatibility:**
+- JSON stored as TEXT (not JSONB) for SQLite compatibility
+- Separate FTS implementations per database engine
 
 ## Repository Structure (Planned)
 
@@ -168,3 +182,4 @@ labmcp/
 - Nix flake must provide importable packages for other repos
 - Use `database/sql` interface for database abstraction
 - File paths in responses should use format `path/to/file.go:123`
+- **Always run `go fmt ./...` before committing Go code**