Fix heading, scope, version placement, and consistency across policy docs

- Rename REPO_POLICIES.md heading from "Development Policies" to
  "Repository Policies" to distinguish from code styleguides
- Move version line above heading per convention
- Add scope statement and links to code styleguide documents
- Add missing Makefile and LICENSE to minimum files list
- Add version lines to all cross-project docs (CODE_STYLEGUIDE*.md,
  GO_HTTP_SERVER_CONVENTIONS.md)
- Clean up CODE_STYLEGUIDE.md heading (was old repo name)
- Update EXISTING_REPO_CHECKLIST.md link text to match new heading

prompts/CODE_STYLEGUIDE_JS.md

@@ -1,3 +1,5 @@
+Version: 2026-02-22
+
 # JavaScript / ECMAScript / ES6
 
 1. Use `const` for everything. If you need to reassign, use `let`. Never use