docs: add Scarf usage-analytics pixel to docs + README

Co-Authored-By: Alex Schapiro <bearsyankees@gmail.com>

docs/usage/cli.mdx

@@ -3,6 +3,10 @@ title: "CLI Reference"
 description: "Command-line options for Strix"
 ---
 
+import { ScarfPixel } from "/snippets/scarf-pixel.mdx";
+
+<ScarfPixel />
+
 ## Basic Usage
 
 ```bash

docs/usage/instructions.mdx

@@ -3,6 +3,10 @@ title: "Custom Instructions"
 description: "Guide Strix with custom testing instructions"
 ---
 
+import { ScarfPixel } from "/snippets/scarf-pixel.mdx";
+
+<ScarfPixel />
+
 Use instructions to provide context, credentials, or focus areas for your scan.
 
 ## Inline Instructions

docs/usage/scan-modes.mdx

@@ -3,6 +3,10 @@ title: "Scan Modes"
 description: "Choose the right scan depth for your use case"
 ---
 
+import { ScarfPixel } from "/snippets/scarf-pixel.mdx";
+
+<ScarfPixel />
+
 Strix offers three scan modes to balance speed and thoroughness.
 
 ## Quick