Migrate omsorgapp to browser SPA, add Docker/CI build setup

- omsorgapp: drop Electron, run as a plain Vite/React browser app; refresh
  token moves to an HttpOnly cookie (omsorgCore), CORS added for the new
  browser origin, document download/preview switched to Blob-based browser
  APIs.
- Add Dockerfiles for omsorgCore, omsorgapp, and omsorgWeb, a docker-compose.yml
  wiring Postgres/MySQL/all three apps together, and a Gitea Actions workflow
  that builds and pushes images to the repo's container registry on push to
  main and on version tags.

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

omsorgWeb/mitarbeiter-app/app.css

@@ -35,10 +35,11 @@ img{display:block;max-width:100%}
 
 form{display:grid;gap:14px}
 label{display:grid;gap:7px;font-weight:800;color:#fff}
-input{
+input,select,textarea{
   width:100%;border:1px solid rgba(170,240,250,.36);border-radius:12px;
   padding:14px;background:rgba(2,11,22,.54);color:#fff;font:inherit;
 }
+textarea{resize:vertical;min-height:90px}
 
 .error{
   padding:12px 14px;border:1px solid rgba(255,130,130,.45);
@@ -111,8 +112,16 @@ input{
 .main-title span{color:var(--cyan)}
 .main-sub{color:var(--muted);font-size:1.05rem;margin:0}
 
+.split-layout{
+  display:grid;
+  grid-template-columns:1fr 1fr;
+  gap:24px;
+  align-items:start;
+}
+
 @media(max-width:860px){
   .dashboard-layout{grid-template-columns:1fr;padding-left:0}
   .sidebar{position:static;width:100%;height:auto}
   .main-content{padding:20px 16px}
+  .split-layout{grid-template-columns:1fr}
 }