Reorganize into monorepo layout, move mitarbeiter-app to legacy reference

Consolidates the previously separate omsorgapp and omsorgCore repos
(each had their own nested .git with GitHub history) plus the old
root-level website/mitarbeiter-app into a single monorepo, matching
the structure already documented in the root CLAUDE.md. Also moves
the PHP employee app aside as omsorgWeb/mitarbeiter-app-legacy/ to
serve as a template for a ground-up rewrite.

Fixes .gitignore in the same pass: the config-secrets/uploads/data
patterns were unanchored (relative to repo root, not depth-agnostic),
so they silently stopped matching once the app moved under omsorgWeb/.
Patterns are now **/-prefixed and cover both mitarbeiter-app and
mitarbeiter-app-legacy, keeping DB/SMTP credentials and uploaded
employee documents out of version control.

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

omsorgapp/electron/backend/config.cjs

@@ -0,0 +1,6 @@
+// Einzige Stelle im Projekt, die die Adresse von omsorgCore kennt.
+// Default passt zum lokalen `dotnet run --project src/OmsorgCore.Api` (http-Profil, Port 5245),
+// überschreibbar per Umgebungsvariable für andere Umgebungen (Produktion, anderer Rechner, ...).
+module.exports = {
+  API_BASE: process.env.OMSORG_CORE_URL || 'http://localhost:5245'
+};