Fix: Missing detectionMethod property in TrackMdRequestParams type causes TypeScript compilation error and build failure.

This commit fixes the issue reported at apps/docs/lib/geistdocs/md-tracking.ts:24

**Bug explanation:**

The `trackMdRequest` function in `apps/docs/lib/geistdocs/md-tracking.ts` destructures `detectionMethod` from its parameter (line 24) and includes it in the JSON body sent to the tracking endpoint (line 38). However, the `TrackMdRequestParams` type definition (lines 6-12) does not include `detectionMethod` as a property.

In `apps/docs/proxy.ts` (line 82-87), `trackMdRequest` is called with `detectionMethod: agentResult.method` when an AI agent is detected, where `agentResult.method` is of type `DetectionMethod | null` from `@/lib/ai-agent-detection`.

This causes an exact TypeScript compilation error confirmed in the build logs:
```
./lib/geistdocs/md-tracking.ts:24:3
Type error: Property 'detectionMethod' does not exist on type 'TrackMdRequestParams'.
```

This error causes the entire `docs` build to fail (`next build` exits with code 1).

**Fix explanation:**

Added `detectionMethod?: DetectionMethod | null` as an optional property to the `TrackMdRequestParams` type, and added the corresponding `import type { DetectionMethod } from "@/lib/ai-agent-detection"` import at the top of the file. The property is optional (`?`) because most call sites (for `.md` URL tracking, `llms.txt` tracking, and header-negotiated tracking) don't pass a `detectionMethod` — only the agent-rewrite tracking path does. The `| null` union matches the `DetectionResult.method` type from `ai-agent-detection.ts`.

Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com>
Co-authored-by: molebox <hello@richardhaines.dev>

Author: vercel[bot]

apps/docs/lib/geistdocs/md-tracking.ts

@@ -1,4 +1,5 @@
 import { siteId } from "@/geistdocs";
+import type { DetectionMethod } from "@/lib/ai-agent-detection";
 
 const PLATFORM_URL = "https://geistdocs.com/md-tracking";
 
@@ -9,6 +10,8 @@ type TrackMdRequestParams = {
   acceptHeader: string | null;
   /** How the markdown was requested: 'md-url' for direct .md URLs, 'header-negotiated' for Accept header */
   requestType?: "md-url" | "header-negotiated" | "agent-rewrite";
+  /** Which detection method identified the AI agent */
+  detectionMethod?: DetectionMethod | null;
 };
 
 /**