feat(manager): add Nexus Instance Manager for demo orchestration

- Complete Flask-based control panel for multi-tenant POS instances
- Dashboard with global stats, system health, and recent demos
- Demo provisioning in 1 click with auto-expiration tracking
- Tenant management: activate/deactivate, reset data, delete
- Health monitoring: PostgreSQL, Redis, disk, memory, systemd services
- Migration orchestration UI for running schema updates across all tenants
- JWT authentication with manager_users table
- Dark theme SPA frontend with real-time search and actions
- systemd service file included

manager/app.py

@@ -0,0 +1,99 @@
+"""Nexus Instance Manager — Flask Application."""
+import os
+import sys
+from datetime import datetime
+from flask import Flask, jsonify, render_template, send_from_directory, request
+
+# Ensure POS modules are importable for tenant_manager reuse
+POS_DIR = os.environ.get("POS_DIR", "/home/Autopartes/pos")
+if POS_DIR not in sys.path:
+    sys.path.insert(0, POS_DIR)
+
+from config import APP_NAME, APP_VERSION
+from blueprints.auth_bp import auth_bp, require_manager_auth
+from blueprints.tenants_bp import tenants_bp
+from blueprints.demos_bp import demos_bp
+from blueprints.health_bp import health_bp
+from blueprints.admin_bp import admin_bp
+
+
+def create_app():
+    app = Flask(
+        __name__,
+        template_folder="templates",
+        static_folder="static"
+    )
+    app.secret_key = os.environ.get("MANAGER_JWT_SECRET", "dev-secret-change-me")
+
+    # Register blueprints
+    app.register_blueprint(auth_bp)
+    app.register_blueprint(tenants_bp)
+    app.register_blueprint(demos_bp)
+    app.register_blueprint(health_bp)
+    app.register_blueprint(admin_bp)
+
+    # ─── Frontend Routes ───────────────────────────────────────────────────
+    @app.route("/")
+    def index():
+        return render_template("index.html")
+
+    @app.route("/login")
+    def login_page():
+        return render_template("index.html")
+
+    @app.route("/dashboard")
+    def dashboard_page():
+        return render_template("index.html")
+
+    @app.route("/tenants")
+    def tenants_page():
+        return render_template("index.html")
+
+    @app.route("/demos")
+    def demos_page():
+        return render_template("index.html")
+
+    @app.route("/health")
+    def health_page():
+        return render_template("index.html")
+
+    @app.route("/migrations")
+    def migrations_page():
+        return render_template("index.html")
+
+    # ─── Static Asset Helpers ──────────────────────────────────────────────
+    @app.route("/static/<path:filename>")
+    def static_files(filename):
+        return send_from_directory("static", filename)
+
+    # ─── API Status ────────────────────────────────────────────────────────
+    @app.route("/api/status")
+    def api_status():
+        return jsonify({
+            "app": APP_NAME,
+            "version": APP_VERSION,
+            "timestamp": datetime.utcnow().isoformat(),
+            "pos_dir": POS_DIR
+        })
+
+    # ─── Error Handlers ────────────────────────────────────────────────────
+    @app.errorhandler(404)
+    def not_found(e):
+        if request.path.startswith("/api/"):
+            return jsonify({"error": "Not found"}), 404
+        return render_template("index.html")
+
+    @app.errorhandler(500)
+    def internal_error(e):
+        if request.path.startswith("/api/"):
+            return jsonify({"error": "Internal server error"}), 500
+        return render_template("index.html")
+
+    return app
+
+
+# Entry point for Gunicorn: gunicorn -w 2 -b 0.0.0.0:5003 app:app
+app = create_app()
+
+if __name__ == "__main__":
+    app.run(host="0.0.0.0", port=5003, debug=True)