paintplus: vendor the app source and rename from EditmaskwithAI

Bring the full EditmaskwithAI application into the repo under paintplus/
(429 files) so the service is self-contained — the installer copies the
vendored source to ~/docker/paintplus/src instead of cloning at runtime.

Rename to PaintPlus (service + branding; app logic untouched):
- services/editmaskwithai.sh -> services/paintplus.sh (register_service
  paintplus, install_paintplus, ~/docker/paintplus, Caddy paintplus:8000,
  Authelia option preserved)
- container names -> paintplus across docker-compose*.yml; dev network
  -> paintplus-network
- browser <title> -> "PaintPlus - AI Image Editor"; README heading ->
  PaintPlus with upstream provenance note
- README utilities table: editmaskwithai -> paintplus

Backend/frontend code (help strings referencing the old container name,
the ai_photo_edit.db filename) is intentionally left as-is to avoid
touching application logic.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nb2vJ8W7bHKx1JXVvpCraH

paintplus/frontend/images/icons/brush_select.svg

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round">
+  <!-- Brush body -->
+  <path d="M18 4L21 7L11 17H8V14L18 4Z"/>
+  <!-- Brush handle -->
+  <path d="M15.5 6.5L17.5 8.5"/>
+  <!-- AI sparkles/selection indicators -->
+  <circle cx="5" cy="5" r="1" fill="currentColor"/>
+  <circle cx="3" cy="9" r="0.75" fill="currentColor"/>
+  <circle cx="7" cy="3" r="0.75" fill="currentColor"/>
+  <!-- Selection dashes around brush tip -->
+  <path d="M6 15L4 17" stroke-dasharray="2,1"/>
+  <path d="M6 19L8 21" stroke-dasharray="2,1"/>
+  <path d="M10 19L12 21" stroke-dasharray="2,1"/>
+</svg>