Fix review issues: front matter, headings, consistency, typos

- Move title and last_modified to YAML front matter (all policy docs)
- Make all document sections H1, subsections H2
- Update version rule to reference front matter format
- Fix "our" → "your" typo in Go styleguide
- Fix Python styleguide numbering (2. → 1.)
- Fix README: "flat collection" → accurate description, remove stale TODO
- Remove Makefile items from code styleguides (repo stuff, not code),
  add note linking to Repository Policies
- Change zerolog → slog in Go styleguide
- Fix JS styleguide npm reference: both work, but use make targets
- Drop .json from healthcheck path, add JSON content-type requirement
- Add Author/License to Go HTTP Server Conventions
- Convert hyperlinks to backtick URLs in checklists for consistency
- Add version/front matter to both checklists

prompts/REPO_POLICIES.md

@@ -1,6 +1,7 @@
-Version: 2026-02-22
-
-# Repository Policies
+---
+title: Repository Policies
+last_modified: 2026-02-22
+---
 
 This document covers repository structure, tooling, and workflow standards. Code
 style conventions are in separate documents:
@@ -14,9 +15,9 @@ style conventions are in separate documents:
 
 ---
 
-- Cross-project documentation (such as this file) must include a
-  `Version: YYYY-MM-DD` line near the top so it can be kept in sync with the
-  authoritative source as policies evolve.
+- Cross-project documentation (such as this file) must include
+  `last_modified: YYYY-MM-DD` in the YAML front matter so it can be kept in sync
+  with the authoritative source as policies evolve.
 
 - **ALL external references must be pinned by cryptographic hash.** This
   includes Docker base images, Go modules, npm packages, GitHub Actions, and