Initial barcode scanner webapp

Camera-based barcode scanner using ZXing for decoding. Requests wide
video (256x2048), rotates to landscape for decoding, applies contrast
boost and tries both HybridBinarizer and GlobalHistogramBinarizer.
Includes camera selector, manual/auto focus controls, and focus slider.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -0,0 +1,25 @@
+DEST ?= dist
+
+SRC = index.html app.mjs
+
+.PHONY: all build deploy clean
+
+all: build
+
+node_modules/.package-lock.json: package.json
+	npm install
+	@touch $@
+
+vendor/zxing.min.js: node_modules/.package-lock.json
+	@mkdir -p vendor
+	cp node_modules/@zxing/library/umd/index.min.js vendor/zxing.min.js
+
+build: vendor/zxing.min.js
+
+deploy: build
+	@mkdir -p $(DEST)/vendor
+	cp $(SRC) $(DEST)/
+	cp vendor/zxing.min.js $(DEST)/vendor/
+
+clean:
+	rm -rf vendor dist