docs: optimize entry doc & remove unused docs (#7922)

Author: yimingjfe

packages/document/docs/en/components/entry-scan-logic.mdx

@@ -0,0 +1,7 @@
+:::tip Entry scanning logic
+- If `src/` itself meets entry criteria → Single-entry application
+- If `src/` does not meet criteria → Scan subdirectories under `src/` → Multi-entry application
+- In single-entry applications, the default entry name is `index`
+
+:::
+