Fix markdown parser dropping local files whose name starts with "http"

[Osamaali313]

Summary

MarkdownParser.extractReferences is meant to extract local file/image references and skip external URLs (per its docstring). It does so with:

if (target.startsWith("http")) continue; // Skip external URLs

But startsWith("http") matches the bare substring, so any local file whose name begins with "http" is silently dropped — e.g. [guide](http-client.md), [notes](https-setup.md), [x](httpie.md). These are relative links that should become file reference edges in the knowledge graph but are discarded, producing missing edges.

Fix

Match an actual URL scheme instead of the "http" prefix:

-      if (target.startsWith("http")) continue; // Skip external URLs
+      // Skip external URLs (scheme://... or protocol-relative //...), but keep
+      // local files whose name merely begins with "http" (e.g. http-client.md).
+      if (/^[a-zA-Z][a-zA-Z0-9+.-]*:\/\//.test(target) || target.startsWith("//")) continue;

This still skips https://example.com, http://…, ftp://…, and protocol-relative //cdn/…, while keeping local files like http-client.md.

Testing

Added a case to the MarkdownParser suite in parsers.test.ts:

it("keeps local files whose name starts with 'http'", () => {
  const content = "[client](http-client.md) and [ext](https://example.com)";
  const refs = parser.extractReferences!("README.md", content);
  expect(refs).toHaveLength(1);
  expect(refs[0].target).toBe("http-client.md");
});

Verified standalone with the exact extractReferences regex/logic:

input: See [HTTP client](http-client.md) and [setup](./setup.md), but ignore [site](https://example.com) and ![img](pic.png).
BEFORE: ["file:./setup.md","image:pic.png"]                       (http-client.md dropped)
AFTER:  ["file:http-client.md","file:./setup.md","image:pic.png"] (kept; external URL still skipped)

The existing "extracts file references" and "skips external URLs in references" tests remain satisfied by the fix.

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