Rename remaining EditmaskwithAI references to PaintPlus

Updates README, Docker/Compose comments and container name, install
script banner, about dialog GitHub link, and a script's cd path to
match the repo's new name.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011g84QwMKwPMFQPwLVnPrQ1

docker-compose.gpu.yml

@@ -1,5 +1,5 @@
 # =============================================================================
-# EditmaskwithAI — GPU Docker Compose (NVIDIA CUDA)
+# PaintPlus — GPU Docker Compose (NVIDIA CUDA)
 #
 # ── PREREQUISITES ─────────────────────────────────────────────────────────────
 #
@@ -66,7 +66,7 @@ services:
         # Increment BUILDID to force pip layers to re-run without full --no-cache:
         #   BUILDID=$(date +%s) docker compose -f docker-compose.gpu.yml up --build
         BUILDID: ${BUILDID:-1}
-    container_name: editmaskwithai-gpu
+    container_name: paintplus-gpu
     ports:
       - "${PORT:-3080}:8000"
     volumes: