fix: preserve directory structure in installation to prevent file overwrites (#169)

Fix installation instructions that caused file overwrites. Adds install.sh script and preserves directory structure. Fixes #164.

install.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+# install.sh — Install claude rules while preserving directory structure.
+#
+# Usage:
+#   ./install.sh <language> [<language> ...]
+#
+# Examples:
+#   ./install.sh typescript
+#   ./install.sh typescript python golang
+#
+# This script copies rules into ~/.claude/rules/ keeping the common/ and
+# language-specific subdirectories intact so that:
+#   1. Files with the same name in common/ and <language>/ don't overwrite
+#      each other.
+#   2. Relative references (e.g. ../common/coding-style.md) remain valid.
+
+set -euo pipefail
+
+RULES_DIR="$(cd "$(dirname "$0")/rules" && pwd)"
+DEST_DIR="${CLAUDE_RULES_DIR:-$HOME/.claude/rules}"
+
+if [[ $# -eq 0 ]]; then
+    echo "Usage: $0 <language> [<language> ...]"
+    echo ""
+    echo "Available languages:"
+    for dir in "$RULES_DIR"/*/; do
+        name="$(basename "$dir")"
+        [[ "$name" == "common" ]] && continue
+        echo "  - $name"
+    done
+    exit 1
+fi
+
+# Always install common rules
+echo "Installing common rules -> $DEST_DIR/common/"
+mkdir -p "$DEST_DIR/common"
+cp -r "$RULES_DIR/common/." "$DEST_DIR/common/"
+
+# Install each requested language
+for lang in "$@"; do
+    lang_dir="$RULES_DIR/$lang"
+    if [[ ! -d "$lang_dir" ]]; then
+        echo "Warning: rules/$lang/ does not exist, skipping." >&2
+        continue
+    fi
+    echo "Installing $lang rules -> $DEST_DIR/$lang/"
+    mkdir -p "$DEST_DIR/$lang"
+    cp -r "$lang_dir/." "$DEST_DIR/$lang/"
+done
+
+echo "Done. Rules installed to $DEST_DIR/"