EPIC: Vendor-Neutral Deployment, Multi-Database Support & Performance Validation

## Overview

This sub-EPIC decouples the deployment ecosystem from vendor-specific constraints, enables native MySQL database support alongside PostgreSQL, makes interactive demos platform-agnostic, and brings Artillery performance testing up to date.

## Goals

1. **Multi-Database Helm Support**:
- Rename database Secret key to `database-password` with backward-compatible fallback to `postgres-password`.
- Generalize `initContainers` to generic `wait-for-db` using dynamic host/port helpers.
- Add native MySQL support in `values.yaml` and `values.schema.json` with latest available versions
- Adapt network policy egress rules dynamically based on backend.
2. **Performance Test Modernization**:
- Bump Artillery test dependencies to latest versions.
- Fix broken test paths and token generation path resolution.
3. **Demo Platform Agnosticism**:
- Clean `demo/environment.yml` of Linux-specific build locks and add standard `requirements.txt` for macOS (Apple Silicon/Intel), Linux, and Windows.

Begin by inspecting the Helm deployment files, especially values.yaml and values.schema.json, to add MySQL alongside PostgreSQL and handle database-password with backward compatibility to postgres-password. Then trace the chart templates for initContainers and network policy egress generation to implement the generic wait-for-db and backend-based rules. Next review demo/environment.yml and requirements.txt for platform-specific lock handling and fix the Artillery dependency/path areas mentioned in the issue. Done means both DB backends are configurable in charts, demo dependencies are cross-platform, and performance test dependencies/paths are updated and runnable.

由索引模型根據 Issue 內容生成。