feat(makefile): add deps, diff, lint targets and fzf-picker fallback

Ports useful quality-of-life targets from DeepSat's coding-rulesets
Makefile, adapted to this repo's two-scope (global + per-project)
structure.

New targets:
  make deps                       Install claude, jq, fzf, ripgrep,
                                  emacs via brew/apt/pacman. Idempotent
                                  (skips already-present tools). For
                                  new machines and VMs.

  make diff LANG=<lang> [PROJECT=<path>]
                                  Show unified diff between repo source
                                  and installed copies in a target
                                  project. CLAUDE.md excluded (seed-
                                  only, diverges by design).

  make lint                       Validate ruleset structure: top-level
                                  headings, 'Applies to:' headers on
                                  rule files, shebangs and exec bits on
                                  hook scripts.

Infrastructure:
  - Help migrated to awk-parsed ##@/## pattern; new targets document
    themselves via a single trailing `## ...` comment.
  - fzf-picker fallback: if PROJECT= is unset, install-lang and diff
    launch fzf over local .git dirs under $HOME. Keeps PROJECT=<path>
    for scripts/automation; only interactive users hit fzf.

  scripts/diff-lang.sh  Walks the file list the installer would copy,
                        diffs each against the target.
  scripts/lint.sh       Standalone ruleset structure validator.

1 files changed, 91 insertions, 0 deletions

diff --git a/scripts/lint.sh b/scripts/lint.sh
new file mode 100755
index 0000000..2956aff
--- /dev/null
+++ b/scripts/lint.sh
@@ -0,0 +1,91 @@
+#!/usr/bin/env bash
+# Validate ruleset structure. Runs from the rulesets repo root.
+# Checks:
+#   - Every .md rule file starts with a top-level heading
+#   - Every rule file has an 'Applies to:' header
+#   - Every language CLAUDE.md has a top-level heading
+#   - Every hook script has a shebang and is executable
+
+set -u
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$REPO_ROOT"
+
+errors=0
+
+warn() {
+  printf '  WARN: %s\n' "$1"
+  errors=$((errors + 1))
+}
+
+check_md_heading() {
+  local f="$1"
+  [ -f "$f" ] || return 0
+  if ! head -1 "$f" | grep -q '^# '; then
+    warn "$f — missing top-level heading"
+  fi
+}
+
+check_md_applies_to() {
+  local f="$1"
+  [ -f "$f" ] || return 0
+  if ! grep -q '^Applies to:' "$f"; then
+    warn "$f — missing 'Applies to:' header"
+  fi
+}
+
+check_hook() {
+  local f="$1"
+  [ -f "$f" ] || return 0
+  if ! head -1 "$f" | grep -q '^#!'; then
+    warn "$f — missing shebang"
+  fi
+  if [ ! -x "$f" ]; then
+    warn "$f — not executable (chmod +x)"
+  fi
+}
+
+echo "Linting rulesets in $REPO_ROOT"
+
+# Generic rules
+for f in claude-rules/*.md; do
+  [ -f "$f" ] || continue
+  check_md_heading "$f"
+  check_md_applies_to "$f"
+done
+
+# Per-language rule files
+for rules_dir in languages/*/claude/rules; do
+  [ -d "$rules_dir" ] || continue
+  for f in "$rules_dir"/*.md; do
+    [ -f "$f" ] || continue
+    check_md_heading "$f"
+    check_md_applies_to "$f"
+  done
+done
+
+# Per-language CLAUDE.md templates
+for claude_md in languages/*/CLAUDE.md; do
+  [ -f "$claude_md" ] || continue
+  check_md_heading "$claude_md"
+done
+
+# Hook scripts
+for h in languages/*/claude/hooks/*.sh languages/*/githooks/*; do
+  [ -f "$h" ] || continue
+  check_hook "$h"
+done
+
+# Shared install/diff/lint scripts (sanity check)
+for s in scripts/*.sh; do
+  [ -f "$s" ] || continue
+  check_hook "$s"
+done
+
+echo "---"
+if [ "$errors" -eq 0 ]; then
+  echo "All checks passed."
+else
+  echo "$errors warning(s)."
+  exit 1
+fi