feat: 添加后台登录验证码、记住密码功能，优化媒体资源与前端规范

- 新增后台登录图形验证码功能，完善登录安全防护
- 新增登录rememberMe参数，控制Refresh Token的会话持久化策略
- 实现OSS私有桶媒体URL自动签名，统一处理图片资源的临时访问签名
- 新增素材库数据库表与上传API，规范媒体资源管理流程
- 统一前端UI图标使用@element-plus/icons-vue，重构布局图标组件
- 登录页新增验证码输入、刷新功能，添加账号记忆与记住密码逻辑
- 更新全套文档，补充API契约、技术决策记录与集成流程说明
- 修复多个业务页面的图标展示问题，新增认证流程相关测试用例

WonderQ-Admin/app/captcha.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+import base64
+import html
+import secrets
+from uuid import uuid4
+
+from .redis_session import AdminSessionStore
+
+CAPTCHA_ALPHABET = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"
+
+
+def _captcha_code(length: int = 4) -> str:
+    return "".join(secrets.choice(CAPTCHA_ALPHABET) for _ in range(length))
+
+
+def _captcha_image(code: str) -> str:
+    lines = "".join(
+        f'<path d="M{secrets.randbelow(150) + 5},{secrets.randbelow(42) + 3} '
+        f'L{secrets.randbelow(150) + 5},{secrets.randbelow(42) + 3}" />'
+        for _ in range(5)
+    )
+    safe_code = html.escape(code)
+    svg = (
+        '<svg xmlns="http://www.w3.org/2000/svg" width="160" height="48" viewBox="0 0 160 48">'
+        '<rect width="160" height="48" rx="4" fill="#f5f7fa"/>'
+        f'<g stroke="#c0c4cc" stroke-width="1" opacity=".8">{lines}</g>'
+        f'<text x="80" y="32" text-anchor="middle" fill="#303133" '
+        'font-family="Arial,sans-serif" font-size="24" font-weight="700" letter-spacing="5">'
+        f"{safe_code}</text></svg>"
+    )
+    encoded = base64.b64encode(svg.encode("utf-8")).decode("ascii")
+    return f"data:image/svg+xml;base64,{encoded}"
+
+
+def create_captcha(store: AdminSessionStore, ttl_seconds: int) -> dict[str, object]:
+    captcha_id = uuid4().hex
+    code = _captcha_code()
+    store.create_captcha(captcha_id, code, ttl_seconds)
+    return {
+        "captchaEnabled": True,
+        "captchaId": captcha_id,
+        "image": _captcha_image(code),
+        "expiresIn": ttl_seconds,
+    }
+
+
+def verify_captcha(store: AdminSessionStore, captcha_id: str, code: str) -> bool:
+    return store.consume_captcha(captcha_id, code)