chore: Deployment version naming and cleanup policy

- **Version naming**: Include date, time, commit hash, and CI run number
  Format: quantengine_YYYYMMDD_HHMMSS_COMMIT_HASH_RUNNUM
- **Cleanup script**: Auto-remove old versions to prevent disk exhaustion
  - Keep 5 most recent by default
  - Remove staging/test versions
  - Can be run weekly via cron or after deployments
  - Supports dry-run mode for validation

Addresses: Disk usage management for long-running CI/CD pipeline

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

scripts/cleanup_old_deployments.sh

@@ -0,0 +1,92 @@
+#!/bin/bash
+# Cleanup old deployment versions to prevent disk exhaustion
+# Deployment version format: quantengine_YYYYMMDD_HHMMSS_COMMIT_HASH_[SEQ]
+# Usage: ./cleanup_old_deployments.sh [keep_count]
+
+set -euo pipefail
+
+DEPLOY_BASE="/home/kjh2064/deployments"
+KEEP_COUNT="${1:-5}"  # Keep 5 most recent versions by default
+
+echo "=========================================="
+echo "🧹 QuantEngine Deployment Cleanup"
+echo "=========================================="
+echo "Base: $DEPLOY_BASE"
+echo "Keeping: $KEEP_COUNT most recent versions"
+echo ""
+
+# Get active deployment
+ACTIVE_LINK="/home/kjh2064/quantengine_active"
+if [ ! -L "$ACTIVE_LINK" ]; then
+    echo "❌ Active link not found: $ACTIVE_LINK"
+    exit 1
+fi
+
+ACTIVE_VERSION=$(readlink -f "$ACTIVE_LINK")
+ACTIVE_NAME=$(basename "$ACTIVE_VERSION")
+
+echo "🔒 Active version: $ACTIVE_NAME"
+echo ""
+
+# List all quantengine deployments sorted by date (newest first)
+echo "📋 Available versions:"
+VERSIONS=$(ls -dt "$DEPLOY_BASE"/quantengine_* 2>/dev/null | head -$((KEEP_COUNT + 1)) | sed 's|.*/||' | sort -r)
+COUNT=0
+
+TO_DELETE=""
+while IFS= read -r version; do
+    VERSION_PATH="$DEPLOY_BASE/$version"
+    SIZE=$(du -sh "$VERSION_PATH" 2>/dev/null | cut -f1)
+
+    COUNT=$((COUNT + 1))
+
+    # Check if this is active
+    if [ "$VERSION_PATH" = "$ACTIVE_VERSION" ]; then
+        echo "  ✓ [$COUNT] $version ($SIZE) [ACTIVE]"
+    elif [ $COUNT -le $KEEP_COUNT ]; then
+        echo "  · [$COUNT] $version ($SIZE)"
+    else
+        echo "  ✗ [$COUNT] $version ($SIZE) [WILL DELETE]"
+        TO_DELETE="$TO_DELETE $VERSION_PATH"
+    fi
+done <<< "$VERSIONS"
+
+# Also check for TEST versions (cleanup more aggressively)
+echo ""
+echo "🧪 Cleaning up TEST versions..."
+TEST_VERSIONS=$(ls -dt "$DEPLOY_BASE"/quantengine_*_TEST 2>/dev/null | head -1 || true)
+if [ -n "$TEST_VERSIONS" ]; then
+    for tv in $TEST_VERSIONS; do
+        if [ "$tv" != "$(readlink -f "$ACTIVE_LINK")" ]; then
+            TEST_SIZE=$(du -sh "$tv" 2>/dev/null | cut -f1)
+            echo "  ✗ $(basename "$tv") ($TEST_SIZE) [STAGING]"
+            TO_DELETE="$TO_DELETE $tv"
+        fi
+    done
+fi
+
+# Execute deletion if not in dry-run mode
+if [ -n "$TO_DELETE" ] && [ "${2:-}" != "dry-run" ]; then
+    echo ""
+    echo "🔄 Removing old versions..."
+    for dir in $TO_DELETE; do
+        if [ -d "$dir" ]; then
+            DIR_NAME=$(basename "$dir")
+            DIR_SIZE=$(du -sh "$dir" | cut -f1)
+            rm -rf "$dir"
+            echo "  ✓ Deleted $DIR_NAME ($DIR_SIZE)"
+        fi
+    done
+
+    FREED=$(du -sh "$DEPLOY_BASE" 2>/dev/null | cut -f1 || echo "unknown")
+    echo ""
+    echo "✅ Cleanup complete. Total size: $FREED"
+else
+    echo ""
+    echo "⏭️  Dry-run mode. Use 'cleanup_old_deployments.sh $KEEP_COUNT' (without dry-run) to delete."
+fi
+
+echo ""
+echo "💡 Recommendation:"
+echo "  - Run weekly via cron: 0 2 * * 0 /home/kjh2064/scripts/cleanup_old_deployments.sh 3"
+echo "  - Or after each successful deployment"