Moves GM player management to PlayerTab

Centralizes all GM controls—add, update, delete player, set RP or renown, reset player passwords—into the PlayerTab for a more intuitive workflow. Removes GM panel logic and duplication from the shop view, clarifies GM access, and improves error feedback on player list loading. Adds a backend health check endpoint and minor UI polish.

.github/workflows/server-healthcheck.yml

@@ -0,0 +1,24 @@
+name: Server Healthcheck
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '*/15 * * * *' # every 15 minutes
+
+jobs:
+  healthcheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '18'
+      - name: Install dependencies
+        run: |
+          cd database
+          npm ci --silent || true
+      - name: Run healthcheck
+        run: |
+          cd database
+          node healthcheck.js