P6: placeholder icon, README, packaged build verified

- assets/icon.png (generated by scripts/make-icon.py) + icon.iconset
  (scripts/gen-iconset.sh); electrobun compiles it to AppIcon.icns
- branding.icon points at the iconset
- README: features, stack, dev/build, rebranding, plaintext-password warning,
  shortcuts, v1 scope
- verified: full production build (ng build + electrobun build) produces a
  launchable BunSCP.app that boots standalone from views://app

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/gen-iconset.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+# Regenerate assets/icon.iconset from assets/icon.png (macOS: sips + iconutil).
+# Electrobun compiles the .iconset folder into AppIcon.icns at build time.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+SRC="assets/icon.png"
+SET="assets/icon.iconset"
+rm -rf "$SET"
+mkdir -p "$SET"
+
+for size in 16 32 128 256 512; do
+	sips -z "$size" "$size" "$SRC" --out "$SET/icon_${size}x${size}.png" >/dev/null
+	sips -z $((size * 2)) $((size * 2)) "$SRC" --out "$SET/icon_${size}x${size}@2x.png" >/dev/null
+done
+
+echo "generated $SET"