Use galaxy4 runner instead of af3-runner

Changed all workflows to use existing org-level galaxy4 runner.

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: j2ho

.github/workflows/check_completion.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   check-jobs:
-    runs-on: [self-hosted, af3-runner]
+    runs-on: [self-hosted, galaxy4]
 
     permissions:
       issues: write

.github/workflows/end_competition.yml

@@ -11,7 +11,7 @@ on:
 jobs:
   end-competition:
     if: github.event.inputs.confirm == 'END'
-    runs-on: [self-hosted, af3-runner]
+    runs-on: [self-hosted, galaxy4]
 
     permissions:
       contents: write

.github/workflows/process_submission.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   validate-and-run:
     if: github.event.label.name == 'submission'
-    runs-on: [self-hosted, af3-runner]
+    runs-on: [self-hosted, galaxy4]
 
     permissions:
       issues: write