Set global canonical base to www.checklyhq.com

Add seo.metatags.canonical so Mintlify emits canonical URLs on the www
apex. Live pages currently emit `https://checklyhq.com/docs/...` (bare
domain), which 301s to www — a non-self-referential canonical. This
fixes the domain for every docs page in one line.

Note: Mintlify appends each page's path without a trailing slash, so
the canonical becomes www + no-slash (still a single 308 to the served
trailing-slash URL). The trailing-slash question is probed separately.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Dgiordano33

docs.json

@@ -9,7 +9,10 @@
   },
   "seo": {
     "title": "Getting started with Checkly - Checkly Docs",
-    "description": "The Application Reliability Platform built for modern engineering teams."
+    "description": "The Application Reliability Platform built for modern engineering teams.",
+    "metatags": {
+      "canonical": "https://www.checklyhq.com"
+    }
   },
   "favicon": "/racoon_favicon.png",
   "customCSS": "/style.css",