Refine assistant layering and plugin source settings

src/constants/agentAssistant.ts

@@ -0,0 +1,8 @@
+// Agent 助手需要覆盖应用内所有普通浮层，因此从 CSS 32 位层级上限向下预留内部顺序。
+const MAX_CSS_Z_INDEX = 2_147_483_647
+
+export const AGENT_ASSISTANT_LAYER_Z_INDEX = {
+  entry: MAX_CSS_Z_INDEX - 2,
+  panel: MAX_CSS_Z_INDEX - 1,
+  overlay: MAX_CSS_Z_INDEX,
+} as const