add CI/CD pipeline with blue-green deployment

GitLab CI runs pytest + ruff on master/MRs, then auto-deploys via SSH.
Blue-green strategy using Docker Compose profiles with an nginx router
on port 5000 for zero-downtime switching between slots.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deploy.sh

@@ -0,0 +1,76 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+COMPOSE="docker compose -f docker-compose.prod.yml"
+LIVE_FILE=".live-slot"
+ROUTER_CONF="router/default.conf"
+
+# ── Determine slots ─────────────────────────────────────────
+
+CURRENT=$(cat "$LIVE_FILE" 2>/dev/null || echo "none")
+
+if [ "$CURRENT" = "blue" ]; then
+    TARGET="green"
+else
+    TARGET="blue"
+fi
+
+echo "==> Current: $CURRENT → Deploying: $TARGET"
+
+# ── Build ───────────────────────────────────────────────────
+
+echo "==> Building $TARGET..."
+$COMPOSE --profile "$TARGET" build
+
+# ── Migrate ─────────────────────────────────────────────────
+
+echo "==> Running migrations..."
+$COMPOSE --profile "$TARGET" run --rm "${TARGET}-app" \
+    python -m padelnomics.migrations.migrate
+
+# ── Start & health check ───────────────────────────────────
+
+echo "==> Starting $TARGET (waiting for health check)..."
+if ! $COMPOSE --profile "$TARGET" up -d --wait; then
+    echo "!!! Health check failed — rolling back"
+    $COMPOSE --profile "$TARGET" stop
+    exit 1
+fi
+
+# ── Switch router ───────────────────────────────────────────
+
+echo "==> Switching router to $TARGET..."
+mkdir -p "$(dirname "$ROUTER_CONF")"
+cat > "$ROUTER_CONF" <<NGINX
+upstream app {
+    server ${TARGET}-app:5000;
+}
+
+server {
+    listen 80;
+
+    location / {
+        proxy_pass http://app;
+        proxy_set_header Host \$host;
+        proxy_set_header X-Real-IP \$remote_addr;
+        proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto \$scheme;
+    }
+}
+NGINX
+
+# Ensure router is running, then reload
+$COMPOSE up -d router
+$COMPOSE exec router nginx -s reload
+
+# ── Stop old slot ───────────────────────────────────────────
+
+if [ "$CURRENT" != "none" ]; then
+    echo "==> Stopping $CURRENT..."
+    $COMPOSE --profile "$CURRENT" stop
+fi
+
+# ── Record live slot ────────────────────────────────────────
+
+echo "$TARGET" > "$LIVE_FILE"
+echo "==> Deployed $TARGET successfully!"