extract startup logic into server/startup.sh for easy customization

Replaces the inline bash -c "..." command in docker-compose with a dedicated
startup.sh script that installs system packages, pip deps, and starts the server.
Add custom setup steps (apt, pip, curl, etc.) in the marked section.

server/startup.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+set -e
+
+# ─── System packages ──────────────────────────────────────────────────────────
+apt-get update -qq
+apt-get install -y --no-install-recommends \
+    curl wget git vim nano htop procps jq less unzip
+
+# ─── Python dependencies ──────────────────────────────────────────────────────
+pip install -q -r /app/requirements.txt
+
+# ─── Custom setup (add your own steps below) ──────────────────────────────────
+# Example:
+#   apt-get install -y --no-install-recommends nodejs npm
+#   pip install -q pandas numpy
+#   curl -fsSL https://example.com/tool | bash
+
+# ─── Start server ─────────────────────────────────────────────────────────────
+exec python -u /app/main.py