docs: update install docs and release automation

scripts/update_homebrew_tap.sh

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+VERSION="${1:?usage: update_homebrew_tap.sh <version> <dmg_path>}"
+DMG_PATH="${2:?usage: update_homebrew_tap.sh <version> <dmg_path>}"
+TAP_DIR="${HOMEBREW_TAP_DIR:-$ROOT_DIR/homebrew-tap}"
+CASK_FILE="$TAP_DIR/Casks/ikeymon.rb"
+
+if [[ ! -d "$TAP_DIR/.git" ]]; then
+  echo "❌ Homebrew tap repo not found at $TAP_DIR"
+  exit 1
+fi
+
+if [[ ! -f "$CASK_FILE" ]]; then
+  echo "❌ Homebrew cask file not found at $CASK_FILE"
+  exit 1
+fi
+
+if [[ ! -f "$DMG_PATH" ]]; then
+  echo "❌ DMG artifact not found at $DMG_PATH"
+  exit 1
+fi
+
+if [[ -n "$(git -C "$TAP_DIR" status --porcelain)" ]]; then
+  echo "❌ Homebrew tap repo has uncommitted changes: $TAP_DIR"
+  exit 1
+fi
+
+SHA256="$(shasum -a 256 "$DMG_PATH" | awk '{print $1}')"
+
+python3 - <<'PY' "$CASK_FILE" "$VERSION" "$SHA256"
+from pathlib import Path
+import re
+import sys
+
+cask_path = Path(sys.argv[1])
+version = sys.argv[2]
+sha256 = sys.argv[3]
+content = cask_path.read_text(encoding="utf-8")
+
+content, version_count = re.subn(r'version "[^"]+"', f'version "{version}"', content, count=1)
+content, sha_count = re.subn(r'sha256 "[^"]+"', f'sha256 "{sha256}"', content, count=1)
+
+if version_count != 1 or sha_count != 1:
+    raise SystemExit("Failed to update version or sha256 in cask file")
+
+cask_path.write_text(content, encoding="utf-8")
+PY
+
+ruby -c "$CASK_FILE" >/dev/null
+
+if git -C "$TAP_DIR" diff --quiet -- "$CASK_FILE"; then
+  echo "ℹ️ Homebrew tap already points to iKeyMon ${VERSION}"
+  exit 0
+fi
+
+git -C "$TAP_DIR" add "$CASK_FILE"
+git -C "$TAP_DIR" commit -m "cask: update ikeymon to ${VERSION}"
+git -C "$TAP_DIR" push origin master
+
+echo "✅ Updated Homebrew tap to iKeyMon ${VERSION}"