ci: replace CompatHelper with dependabot for Julia deps (#115)

Dependabot now covers Julia dependency compat bumps across all Project.toml locations, making the CompatHelper workflow redundant.

Co-authored-by: Claude <noreply@anthropic.com>

Author: sethaxen

.github/dependabot.yml

@@ -5,3 +5,14 @@ updates:
     directory: "/" # Location of package manifests
     schedule:
       interval: "monthly"
+  - package-ecosystem: "julia"
+    directories: # Location of Julia projects
+      - "/"
+      - "/docs"
+    schedule:
+      interval: "daily"
+    groups:
+      # Group all Julia package updates into a single PR:
+      all-julia-packages:
+        patterns:
+          - "*"