docs: document favicon generation; chore: add generate-favicon script and yarn task

tools/generate-favicon.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Generates a multi-size favicon.ico from public/favicon.svg
+# Dependencies:
+#   - rsvg-convert (from librsvg)
+#   - ImageMagick (magick)
+# macOS install:
+#   brew install librsvg imagemagick
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+ROOT_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+SVG_PATH="${ROOT_DIR}/public/favicon.svg"
+OUT_ICO_PATH="${ROOT_DIR}/public/favicon.ico"
+
+if ! command -v rsvg-convert >/dev/null 2>&1; then
+  echo "ERROR: rsvg-convert not found. Install with: brew install librsvg" >&2
+  exit 1
+fi
+if ! command -v magick >/dev/null 2>&1; then
+  echo "ERROR: ImageMagick (magick) not found. Install with: brew install imagemagick" >&2
+  exit 1
+fi
+
+tmp_dir="$(mktemp -d)"
+cleanup() { rm -rf "${tmp_dir}"; }
+trap cleanup EXIT
+
+sizes=(16 32 48 64)
+pngs=()
+for s in "${sizes[@]}"; do
+  out_png="${tmp_dir}/favicon-${s}.png"
+  rsvg-convert -w "${s}" -h "${s}" "${SVG_PATH}" -o "${out_png}"
+  pngs+=("${out_png}")
+done
+
+magick "${pngs[@]}" "${OUT_ICO_PATH}"
+echo "Generated ${OUT_ICO_PATH}"
+
+