Serve the MealQuest favicon instead of the browser default (Maestro 7c778111)

index.html linked only the apple-touch-icon, so browsers fell back to a
default favicon. generate-icons now also writes favicon.ico (16/32/48
PNG-in-ICO) and 16/32 px PNG favicons from the v1 logo; index.html links
them, and the service worker precaches every icon and favicon so the
offline shell keeps them (the glob covers the manifest icons, so the
plugin no longer injects them a second time).

pwa.test.ts asserts the build ships the favicons at the right sizes,
links them from index.html, and precaches each icon exactly once.

Task: 7c778111-c615-4437-a3f6-0e36bcb97e63

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/scripts/generate-icons/main.go

@@ -1,5 +1,5 @@
-// Command generate-icons writes the PWA icons in web/public from the
-// MealQuest logo. Run it from the repository root:
+// Command generate-icons writes the PWA icons and favicons in web/public from
+// the MealQuest logo. Run it from the repository root:
 //
 //	go run ./web/scripts/generate-icons
 //
@@ -9,10 +9,13 @@
 package main
 
 import (
+	"bytes"
+	"encoding/binary"
 	"fmt"
 	"image"
 	"image/color"
 	"image/png"
+	"io"
 	"math"
 	"os"
 	"path/filepath"
@@ -27,6 +30,9 @@ const (
 	maskableScale = 0.66
 )
 
+// faviconSizes are the images packed into favicon.ico.
+var faviconSizes = []int{16, 32, 48}
+
 func main() {
 	if err := run(); err != nil {
 		fmt.Fprintln(os.Stderr, "generate-icons:", err)
@@ -49,6 +55,8 @@ func run() error {
 		{"icons/icon-192.png", resized(logo, 192)},
 		{"icons/icon-512.png", resized(logo, 512)},
 		{"icons/icon-maskable-512.png", maskable(logo, 512)},
+		{"icons/favicon-16.png", resized(logo, 16)},
+		{"icons/favicon-32.png", resized(logo, 32)},
 		{"apple-touch-icon.png", resized(logo, 180)},
 	}
 	for _, out := range outputs {
@@ -58,9 +66,53 @@ func run() error {
 		}
 		fmt.Printf("wrote %s (%dx%d)\n", path, out.image.Rect.Dx(), out.image.Rect.Dy())
 	}
+	ico, err := favicon(logo)
+	if err != nil {
+		return err
+	}
+	path := filepath.Join(public, "favicon.ico")
+	if err := os.WriteFile(path, ico, 0o644); err != nil {
+		return err
+	}
+	fmt.Printf("wrote %s (%v)\n", path, faviconSizes)
 	return nil
 }
 
+// favicon is an ICO file holding the logo at each of faviconSizes as an
+// embedded PNG: a 6-byte header, a 16-byte directory entry per image, then
+// the images.
+func favicon(logo image.Image) ([]byte, error) {
+	var images [][]byte
+	for _, size := range faviconSizes {
+		var buf bytes.Buffer
+		if err := encode(&buf, resized(logo, size)); err != nil {
+			return nil, fmt.Errorf("encode favicon %dx%d: %w", size, size, err)
+		}
+		images = append(images, buf.Bytes())
+	}
+	var out bytes.Buffer
+	le := binary.LittleEndian
+	out.Write(le.AppendUint16(nil, 0))                   // reserved
+	out.Write(le.AppendUint16(nil, 1))                   // type: icon
+	out.Write(le.AppendUint16(nil, uint16(len(images)))) // image count
+	offset := 6 + 16*len(images)
+	for i, size := range faviconSizes {
+		out.WriteByte(byte(size))           // width
+		out.WriteByte(byte(size))           // height
+		out.WriteByte(0)                    // palette size: none
+		out.WriteByte(0)                    // reserved
+		out.Write(le.AppendUint16(nil, 1))  // colour planes
+		out.Write(le.AppendUint16(nil, 32)) // bits per pixel
+		out.Write(le.AppendUint32(nil, uint32(len(images[i]))))
+		out.Write(le.AppendUint32(nil, uint32(offset)))
+		offset += len(images[i])
+	}
+	for _, img := range images {
+		out.Write(img)
+	}
+	return out.Bytes(), nil
+}
+
 // load decodes the logo. The file is a PNG despite its .jpg name, so the
 // format is sniffed rather than taken from the extension.
 func load(path string) (image.Image, error) {
@@ -84,14 +136,18 @@ func save(path string, img image.Image) error {
 	if err != nil {
 		return err
 	}
-	enc := png.Encoder{CompressionLevel: png.BestCompression}
-	if err := enc.Encode(f, img); err != nil {
+	if err := encode(f, img); err != nil {
 		f.Close()
 		return fmt.Errorf("encode %s: %w", path, err)
 	}
 	return f.Close()
 }
 
+func encode(w io.Writer, img image.Image) error {
+	enc := png.Encoder{CompressionLevel: png.BestCompression}
+	return enc.Encode(w, img)
+}
+
 func resized(logo image.Image, size int) *image.RGBA {
 	dst := image.NewRGBA(image.Rect(0, 0, size, size))
 	draw.CatmullRom.Scale(dst, dst.Rect, logo, logo.Bounds(), draw.Src, nil)