Extraction: configurable load paths and multi-gemspec monorepo discovery

[TristanKruse]

Context

The real-world audit against Rails exposed a resolution gap. When the repository root contains multiple gems, imports between sibling gems are currently classified as external. For example,
equire 'active_support' from Action Pack is not resolved to �ctivesupport/lib/active_support.rb because extraction currently searches only the repository root and its top-level lib directory.

Goal

Support Ruby monorepos and non-standard project layouts without executing application code or gemspecs.

Starting approach

• Discover *.gemspec files under the project root.
• Add each existing sibling lib directory to the internal feature search roots.
• Allow users to supply additional explicit load paths for layouts such as components//lib or plugins//lib.
• Normalize and deduplicate paths deterministically.
• Include analysis-affecting load-path options in the graph-cache key.

The public API shape should remain idiomatic and follow the existing options-bag/fluent conventions.

Acceptance criteria

• A multi-gem fixture resolves a cross-gem
  equire as an internal edge.
• Explicit custom load paths resolve internal imports.
• A normal single-gem project behaves exactly as before.
• Gemspec files are discovered but never evaluated.
• Windows and POSIX path behavior are covered.
• Cache reuse and invalidation remain correct.
• README/API documentation explains automatic discovery, explicit paths, and limitations.

Observed during the 0.0.1 real-world audit of Rails (3,445 Ruby files).