docs: add domain glossary and agent skill configuration

- CONTEXT.md: domain glossary with 20+ terms, relationships, example
  dialogue, flagged ambiguities, and known issues from grill-with-docs
- docs/agents/: issue tracker (GitHub), triage labels (defaults), and
  domain doc layout (single-context) for engineering skills
- CLAUDE.md: append Agent skills section pointing to docs/agents/
- .gitignore: whitelist CONTEXT.md and docs/agents/*.md

.gitignore

@@ -59,6 +59,8 @@ oldreference/
 !/docs/architecture/*.md
 !/CLAUDE.md
 !/AGENTS.md
+!/CONTEXT.md
+!/docs/agents/*.md
 !/问题.md
 !/.planning/**/*.md
 !/src/main/prompt-builder/**/*.md