fix: sample report writes to tmp/snap_diff/index.html (matches action)

The upload-screenshots action checks tmp/snap_diff/ for the HTML report.
The sample script was writing to tmp/sample_report.html instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pftg

scripts/generate_sample_report.rb

@@ -9,7 +9,7 @@
 require "capybara/screenshot/diff"
 require "capybara_screenshot_diff/reporters/html"
 
-output_path = File.expand_path("../tmp/sample_report.html", __dir__)
+output_path = File.expand_path("../tmp/snap_diff/index.html", __dir__)
 
 # Build real comparisons using the gem's own ImageCompare.
 # Each pair gets a unique copy of the base image to avoid annotation file conflicts.