feat: restore /close-issue slash command via symlink (#1344)

- Create symlink .claude/commands/close-issue.md → knowledge/procedures/close-issue-procedure.md
- Enables Claude Code slash command autocomplete and ergonomics
- Maintains provider-agnostic knowledge base as single source of truth
- No duplication: symlink ensures consistency across all AI providers

This "tracer bullet" approach meets halfway between pure natural language
invocation and dedicated slash commands, leveraging Claude Code's UX while
preserving AI provider agnosticism.

Closes #1343

Author: atxtechbro

.claude/commands/close-issue.md

@@ -0,0 +1 @@
+../../knowledge/procedures/close-issue-procedure.md