fix(dashboard): polish form and disclosure controls

[Fridemn]

修复新版 Dashboard 中部分组件样式未覆盖、交互控件错位以及下拉菜单出现空白选项的问题，统一相关组件的视觉与无障碍行为。

Summary / 改动概述

• 修复首次提示弹窗中 Markdown 外部链接被渲染为原生按钮样式的问题，使 GitHub、官网、用户协议和邮箱链接保持统一的链接外观。
• 新增通用 DisclosureButton 组件，统一折叠按钮的尺寸、对齐、点击区域、图标方向和焦点状态。
• 优化机器人创建、插件命令、函数工具、人格设置等位置的折叠控件布局。
• 为折叠按钮补充 aria-expanded、可访问名称和多语言文案。
• 修复动态配置下拉框无条件生成空白选项的问题；仅在当前配置值无法匹配枚举项时保留隐藏占位。
• 增加 Markdown 链接、折叠按钮和枚举下拉框的回归测试。

Verification / 验证方式

• GitHub Actions：Check Dashboard 已通过
  • TypeScript typecheck
  • TypeScript / React lint
  • Style lint
  • Formatting check
  • Tests and coverage thresholds
  • Production bundle build
• 已增加相关组件的回归测试，覆盖正常状态及旧配置异常值兼容场景。

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Checklist / 检查清单

• This change is not a breaking change. / 此改动不是破坏性变更。
• I have verified the change locally (and provided logs/screenshots above). / 我已在本地验证并在上方提供日志/截图。
• If workflows are changed, I attached at least one related Actions run link. / 如果修改了工作流，我已附上至少一个相关 Actions 运行链接。
• If dependencies are updated, lockfiles are updated accordingly (src-tauri/Cargo.lock, lockfiles under changed package dirs). / 如果引入或升级依赖，已同步更新相关 lock 文件（如 src-tauri/Cargo.lock、对应包目录中的 lock 文件）。
• This PR does not include malicious code. / 此 PR 不包含恶意代码。

Summary by Sourcery

Unify dashboard disclosure, markdown link, and enum select controls for consistent layout and accessibility.

Bug Fixes:

• Prevent dynamic enum selects from rendering an empty placeholder option when the current value is valid.
• Ensure external markdown links render as styled link controls instead of default button appearance.

Enhancements:

• Introduce a reusable DisclosureButton component with standardized styling, focus behavior, and accessible labelling for collapsible UI sections.
• Align command, tool, platform, and persona collapsible layouts around the new disclosure control, including improved keyboard and screen reader affordances.

Tests:

• Extend markdown, shared primitives, and dynamic config form tests to cover external link controls, disclosure behavior, and enum-select placeholder handling.

[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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