Add analyze subcommand that scans .typ files for @preview and @local
imports, follows transitive deps of @local packages, and outputs
structured JSON to stdout without downloading or copying anything.

- Restructure CLI to subcommands (gather/analyze) with backwards compat
- Support reading config from stdin with `-`
- Move all println! to eprintln! so stdout is clean for JSON output
- Add AnalyzeResult/ImportInfo types with serde Serialize
- Deduplicate imports by (namespace, name, version), direct wins