ci: check github source links through raw.githubusercontent.com

Even paced, github.com still answered some source page requests with 503. Remapping blob links to the raw CDN checks that the same files exist without hitting the rate limit.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: nos1dot618

lychee.toml

@@ -19,14 +19,19 @@ timeout = 20
 # 429 means rate limited, not broken.
 accept = ["200..=299", "429"]
 
+# Check source files on raw.githubusercontent.com, a CDN, instead of their
+# github.com pages: github.com rate-limits a burst of page requests with 503.
+remap = [
+    '^https://github\.com/([^/]+/[^/]+)/blob/(.+)$ https://raw.githubusercontent.com/$1/$2',
+]
+
 exclude = [
     # The site's own absolute URLs (canonical links, the sitemap) point at the
     # deployed copy; the same pages are checked as local files instead.
     '^https://lambda-discipline\.github\.io',
 ]
 
-# github.com answers a burst of page requests (every example links to its
-# source there) with 503 Service Unavailable, so pace requests to it.
+# Pace the remaining github.com requests (repository and organization pages).
 [hosts."github.com"]
 concurrency = 2
 request_interval = "500ms"