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/italic.svg

@@ -0,0 +1,2 @@
+<?xml version="1.0" encoding="iso-8859-1"?>
+<svg width="1em" height="1em" viewBox="0 0 16 16" class="bi bi-type-italic" fill="currentColor" xmlns="http://www.w3.org/2000/svg"><path d="M7.991 11.674L9.53 4.455c.123-.595.246-.71 1.347-.807l.11-.52H7.211l-.11.52c1.06.096 1.128.212 1.005.807L6.57 11.674c-.123.595-.246.71-1.346.806l-.11.52h3.774l.11-.52c-1.06-.095-1.129-.211-1.006-.806z"/></svg>