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>

omsorgCore/.config/dotnet-tools.json

@@ -0,0 +1,12 @@
+{
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "dotnet-ef": {
+      "version": "8.0.10",
+      "commands": [
+        "dotnet-ef"
+      ]
+    }
+  }
+}