ci(canary): run canary every 15 minutes instead of hourly (#1707)

Tightens the canary schedule from '0 * * * *' (hourly) to '*/15 * * * *'
so breakages in our dependencies or the service (e.g. the CDK schema
mismatch that broke deployments) surface within ~15 min instead of up to
an hour later.

Runs stay serialized via the existing 'canary' concurrency group, so a
run that overruns 15 min queues the next one rather than overlapping.

Author: notgitika

.github/workflows/canary.yml

@@ -1,9 +1,10 @@
 name: Canary
 
 on:
-  # Run once an hour
+  # Run every 15 minutes to catch dependency/service breakages (e.g. CDK
+  # schema mismatches) quickly instead of up to an hour later.
   schedule:
-    - cron: '0 * * * *'
+    - cron: '*/15 * * * *'
   workflow_dispatch:
     inputs:
       aws_region: