Add a new engineering skill that creates or refreshes a bounded project
memory file to serve as a navigation map for repository exploration.
The skill follows a disciplined search procedure that:
- Uses fd/rg for inventory before broad file reads
- Classifies project type with evidence citations
- Reads selectively with per-file content caps
- Indexes via tree-sitter/LSP/rg before browsing source
- Caches results in .agent/project-context.md
References the skill in README.md, common/README.md, and
common/engineering/README.md.
