fix(ci): retarget 8 jobs from dead rune-infra-pi label to live rune-desktop runner

New submissions (issues/PRs) were stuck queued forever: auto-label.yml's
priority-gate + demand-comment jobs declared runs-on: rune-infra-pi, a
runner that no longer exists anywhere (registration list shows only
rune-desktop on gitea-desktop-runner). Every issue or PR filed since the
label went dark sat unprocessed — which is exactly the 'new submissions
not working' symptom.

Retargeted (sed, 8 occurrences across 4 workflows):
- auto-label.yml (2): priority gate, demand comment
- auto-backup.yml (1), auto-update-gitea.yml (1), auto-version.yml (1)
- maintenance.yml (5)

Verified live: probe issue + probe PR + probe branch all created AND
processed successfully through the API (submissions themselves work; it
was the responder workflows that were orphaned). Probe artifacts cleaned
up. The stuck queued runs 18178/18183 will drain once this lands.

.gitea/workflows/auto-backup.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   backup:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       # actions/checkout v4.2.2, pinned to the audited upstream tag commit.
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683

.gitea/workflows/auto-label.yml

@@ -12,7 +12,7 @@ jobs:
   # a demand comment — filing is not complete until prioritized.
   priority-gate:
     if: github.event_name == 'issues' && github.event.action != 'labeled' && github.event.issue.state == 'open'
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - name: Enforce priority label
         uses: actions/github-script@v7
@@ -44,7 +44,7 @@ jobs:
             });
 
   auto-label:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - name: Analyze and label
         uses: actions/github-script@v7

.gitea/workflows/auto-update-gitea.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   update-gitea:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - name: Check current Gitea version
         id: current

.gitea/workflows/auto-version.yml

@@ -11,7 +11,7 @@ permissions: write-all
 
 jobs:
   release:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - uses: actions/checkout@v4
         with:

.gitea/workflows/maintenance.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   lint-and-format:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - uses: actions/checkout@v4
       - name: Lint Python files
@@ -18,7 +18,7 @@ jobs:
           ruff format shared/ src/ || true
 
   canary-suite:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - uses: actions/checkout@v4
       - name: Run all canaries
@@ -37,7 +37,7 @@ jobs:
           exit $FAILED
 
   best-practices:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - uses: actions/checkout@v4
       - name: Check best practices
@@ -72,7 +72,7 @@ jobs:
           grep -rn "TODO\|FIXME\|HACK\|XXX" shared/ src/ --include="*.py" | head -10 || echo "  Clean"
 
   documentation-check:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - uses: actions/checkout@v4
       - name: Check documentation coverage
@@ -113,7 +113,7 @@ jobs:
   # push-triggered safety net in auto-version.yml. Detects master/tag drift
   # and files a deduped issue — it never auto-releases without the PR flow.
   release-drift-reconciliation:
-    runs-on: rune-infra-pi
+    runs-on: rune-desktop
     steps:
       - uses: actions/checkout@v4
         with: