fix(ci): revert runner labels to ubuntu-latest — runners do not match [self-hosted, linux, x64]

The self-hosted runners register as 'ubuntu-latest', not '[self-hosted, linux, x64]'.
All recent CI runs (#43-49) have been stuck in 'queued' because no runner
matches the label. Run #42 (commit 38279ed) passed all 4 stages using
'runs-on: ubuntu-latest'.

This restores the working runner configuration while keeping the proven
inline SDK setup approach.

.gitea/workflows/release.yml

@@ -16,7 +16,7 @@ jobs:
   # ── Lint (gate) ─────────────────────────────────────────────
   lint:
     name: Lint
-    runs-on: [self-hosted, linux, x64]
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -60,7 +60,7 @@ jobs:
   # ── Test (gate) ──────────────────────────────────────────────────
   test:
     name: Test
-    runs-on: [self-hosted, linux, x64]
+    runs-on: ubuntu-latest
     needs: [lint]
     steps:
       - name: Checkout
@@ -101,7 +101,7 @@ jobs:
   # the runner host, causing the job to stall indefinitely on docker pull.
   build-android:
     name: Build Android Release
-    runs-on: [self-hosted, linux, x64]
+    runs-on: ubuntu-latest
     needs: [test]
     steps:
       - name: Checkout
@@ -230,7 +230,7 @@ jobs:
   # ── iOS release build ───────────────────────────────────────
   build-ios:
     name: Build iOS Release
-    runs-on: [self-hosted, linux, x64]
+    runs-on: ubuntu-latest
     needs: [test]
     steps:
       - name: Checkout
@@ -247,7 +247,7 @@ jobs:
   # ── Publish Gitea Release ────────────────────────────────────
   publish-release:
     name: Publish Release
-    runs-on: [self-hosted, linux, x64]
+    runs-on: ubuntu-latest
     needs: [build-android]
     steps:
       - name: Checkout