feat(specs): apply hierarchical specs changes and archive

Apply delta specs from hierarchical-specs change to main specs:
- Update cli/ specs (archive, list, show, spec, validate, view) to support
  hierarchical spec IDs and recursive discovery
- Create new specs for hierarchical-spec-discovery and hierarchical-spec-resolution
- Archive hierarchical-specs change with date prefix (2026-03-13)

Specs now support:
- Recursive discovery of specs at any nesting depth
- Hierarchical spec IDs (e.g., cli/show) alongside flat IDs (e.g., cli-show)
- Subtree filtering (e.g., list specs under cli/)
- Cross-platform path normalization
- Fuzzy matching for hierarchical IDs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: victorhsb