feat(ci): migrate all workflows to GKE self-hosted runners

Swap all `runs-on: ubuntu-latest` to `runs-on: arc-runner-set` all jobs.
The ARM docker build job in docker.yml uses `${{ matrix.runner }}`
and is left untouched since the GKE runner pool is x86_64 only.

Runners are backed by ARC (Actions Runner Controller) on a GKE cluster
with a spot preemptible node pool that scales based on job demand.

Use the baked Electron dependencies for the desktop E2E job.

.github/workflows/docker.yml

@@ -37,12 +37,12 @@ jobs:
       matrix:
         include:
           - arch: amd64
-            runner: ubuntu-latest
+            runner: arc-runner-set
             platform: linux/amd64
             cache-from: type=gha,scope=docker-amd64
             cache-to: type=gha,mode=max,scope=docker-amd64
           - arch: arm64
-            runner: ubuntu-24.04-arm
+            runner: arc-runner-arm64
             platform: linux/arm64
             cache-from: type=gha,scope=docker-arm64
             cache-to: type=gha,mode=max,scope=docker-arm64
@@ -143,12 +143,12 @@ jobs:
       matrix:
         include:
           - arch: amd64
-            runner: ubuntu-latest
+            runner: arc-runner-set
             platform: linux/amd64
             cache-from: type=gha,scope=docker-amd64
             cache-to: type=gha,mode=max,scope=docker-amd64
           - arch: arm64
-            runner: ubuntu-24.04-arm
+            runner: arc-runner-arm64
             platform: linux/arm64
             cache-from: type=gha,scope=docker-arm64
             cache-to: type=gha,mode=max,scope=docker-arm64
@@ -216,7 +216,7 @@ jobs:
   # ---------------------------------------------------------------------------
   merge:
     if: github.repository == 'NousResearch/hermes-agent' && (github.event_name == 'push' && github.ref == 'refs/heads/main' || github.event_name == 'release')
-    runs-on: ubuntu-latest
+    runs-on: arc-runner-set
     needs: [publish]
     timeout-minutes: 10
     environment: container-publish