feat(server): improve markdown parse (#14580)

#### PR Dependency Tree


* **PR #14580** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Markdown conversion now reports lists of known-unsupported and unknown
block identifiers encountered during parsing, and separates them from
the main markdown output.

* **Bug Fixes**
  * Improved error handling and logging around markdown parsing.

* **Tests**
* Updated tests and snapshots to reflect the new block-list fields and
the adjusted markdown output.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/native/index.d.ts

@@ -83,6 +83,8 @@ export interface NativeCrawlResult {
 export interface NativeMarkdownResult {
   title: string
   markdown: string
+  knownUnsupportedBlocks: Array<string>
+  unknownBlocks: Array<string>
 }
 
 export interface NativePageDocContent {