feat(rules): rules/ directory symlinked into ~/.claude like the other dirs

Claude Code loads modular rule files from ~/.claude/rules/ (user scope,
recursive, markdown, optional paths: frontmatter for lazy path-scoped
loading — stable, symlink-supported). The repo had no rules/ at all, so
the ctx7 setup had created ~/.claude/rules as a REAL directory outside
version control — invisible to the repo, unreproducible on a new machine.

- rules/README.md — doctrine: one rule per file; paths:-scoped extraction
  is the token win, always-on doctrine stays in CLAUDE.md
- link.sh — rules added to the symlinked-dirs loop
- .gitignore — rules/context7.md ignored (machine-owned: `ctx7 setup`
  (re)writes it, same treatment as skills/find-docs/)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XpphkdTosUzokBDNG7PToS

link.sh

@@ -20,7 +20,7 @@ link_file() {
 link_file "$REPO/CLAUDE.md"     "$CLAUDE/CLAUDE.md"
 link_file "$REPO/settings.json" "$CLAUDE/settings.json"
 
-for item in hooks agents skills lib templates; do
+for item in hooks agents skills lib templates rules; do
   target="$CLAUDE/$item"
   if [ -L "$target" ]; then
     if [ "$(readlink "$target")" = "$REPO/$item" ]; then