Add PR validation before creating PRs

- Create validate-pr.sh: runs shellcheck, JSON/YAML/Python syntax checks
- Update gitea-pr.sh: runs validation before creating PR
- Update CLAUDE.md: document PR review policy
  - ~/.claude repo: linting/validation only
  - Code repos: full code-reviewer agent review

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -98,6 +98,14 @@ Notes:
 - Stash uncommitted state files before switching branches
 - Delete feature branches after merge
 - Gitea token stored at `~/.config/gitea-token`
+- PRs show as "closed" (not "merged") after rebase - expected
+
+### PR Review Policy
+
+| Repo Type | Review Process |
+|-----------|----------------|
+| ~/.claude | Linting/validation only (shellcheck, JSON/YAML syntax, Python syntax) |
+| Code repos | Full review via code-reviewer agent before user approval |
 
 ## Component Formats