feat: share the no-binaries gate, promoted out of testsAndMisc

Every repo should give the same answer to "may this file be committed?",
and until now only testsAndMisc had a checker. signal-bot is public, had
three binary SQLite files in its history before anyone noticed, and
holds a private message database one `git add -f` away from the same
fate -- so .gitignore is evidently not the whole defence.

Two changes from the testsAndMisc original: sqlite3-wal and sqlite3-shm
are blocked by name, because a live SQLite database is three files and
blocking only the first blocks nothing useful; and the error message no
longer names a testsAndMisc-specific directory to move things to.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015d48t4qsQLBJnDwDeo2Nom

scripts/check_no_binaries.sh

@@ -0,0 +1,96 @@
+#!/bin/bash
+
+# ============================================================================
+# Block binary and image files from being committed.
+#
+# Promoted here from testsAndMisc/meta/scripts so every repo gets the same
+# answer to "may this file be committed?". signal-bot is a public repository
+# that had three binary SQLite files in its history before this existed, and
+# it also holds a private message database one `git add -f` away from the
+# same fate -- so the rule wants enforcing everywhere, not per repo.
+#
+# Exceptions live in .binary-allowlist in the repo root, one glob per line.
+# ============================================================================
+
+set -euo pipefail
+
+readonly ALLOWLIST_FILE=".binary-allowlist"
+
+readonly BLOCKED_EXTENSIONS=(
+	# Images
+	png jpg jpeg gif webp svg ico bmp tiff tif psd
+	# Audio/Video
+	mp3 mp4 wav avi mkv flac ogg wma aac m4a mov wmv flv
+	# Archives
+	zip tar gz tgz bz2 xz 7z rar
+	# Documents
+	pdf doc docx xls xlsx ppt pptx
+	# Fonts
+	ttf woff woff2 eot otf
+	# Compiled / binary
+	o so a exe dll dylib pyc pyo class
+	# Data. sqlite3-wal and -shm are spelled out because a live database is
+	# three files, and blocking only the first one blocks nothing useful.
+	apkg bin flat db sqlite sqlite3 sqlite3-wal sqlite3-shm
+)
+
+allowed_patterns=()
+
+build_pattern() {
+	local pattern="" ext
+	for ext in "${BLOCKED_EXTENSIONS[@]}"; do
+		if [[ -z "$pattern" ]]; then
+			pattern="\\.(${ext}"
+		else
+			pattern="${pattern}|${ext}"
+		fi
+	done
+	printf '%s)$' "$pattern"
+}
+
+load_allowlist() {
+	[[ -f "$ALLOWLIST_FILE" ]] || return 0
+	local line
+	while IFS= read -r line; do
+		[[ "$line" =~ ^[[:space:]]*# ]] && continue
+		[[ -z "${line// /}" ]] && continue
+		allowed_patterns+=("$line")
+	done <"$ALLOWLIST_FILE"
+}
+
+is_allowed() {
+	local file="$1" pat
+	for pat in "${allowed_patterns[@]+"${allowed_patterns[@]}"}"; do
+		# shellcheck disable=SC2254
+		case "$file" in
+		$pat) return 0 ;;
+		esac
+	done
+	return 1
+}
+
+main() {
+	local pattern found=0 file
+	pattern="$(build_pattern)"
+	load_allowlist
+
+	for file in "$@"; do
+		# Untracked or deleted paths are not this gate's business.
+		git ls-files --error-unmatch "$file" >/dev/null 2>&1 || continue
+		grep -qiE "$pattern" <<<"$file" || continue
+		is_allowed "$file" && continue
+		echo "BLOCKED: $file"
+		found=1
+	done
+
+	if [[ "$found" -eq 1 ]]; then
+		echo ""
+		echo "ERROR: binary/image files must not be committed."
+		echo "Options:"
+		echo "  1. Keep them outside the repo (preferred)."
+		echo "  2. Add a glob to $ALLOWLIST_FILE, for genuinely essential files."
+		exit 1
+	fi
+}
+
+main "$@"