ci(test-backend): run on ubuntu-latest + rustup instead of rust:1-slim

act_runner runs JS actions (checkout/cache) with node inside the job
container; rust:1-slim ships no node, so every JS action failed with
exit 127 ("node: not found"). Drop the container, run on the
node-equipped ubuntu-latest image, install Rust via rustup. The postgres
service is still reachable by name (act_runner containerises the job).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yml

@@ -10,8 +10,6 @@ on:
 jobs:
   test-backend:
     runs-on: ubuntu-latest
-    container:
-      image: rust:1-slim
     services:
       postgres:
         image: postgres:16-alpine
@@ -28,10 +26,18 @@ jobs:
       DATABASE_URL: postgres://mangalord:mangalord@postgres:5432/mangalord
     steps:
       - uses: actions/checkout@v4
-      - name: Install build deps
+      # ubuntu-latest has node (so JS actions like checkout/cache run) but no
+      # Rust. We intentionally avoid `container: rust:1-slim` because act_runner
+      # runs JS actions with node *inside* the job container, and the slim Rust
+      # image ships no node (checkout would fail with exit 127).
+      - name: Install Rust + build deps
         run: |
-          apt-get update
+          set -eu
-          apt-get install -y --no-install-recommends pkg-config libssl-dev ca-certificates
+          SUDO=""; [ "$(id -u)" = "0" ] || SUDO="sudo"
+          $SUDO apt-get update
+          $SUDO apt-get install -y --no-install-recommends pkg-config libssl-dev ca-certificates curl
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile minimal --default-toolchain stable
+          echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
       - name: Cache cargo registry and target
         uses: actions/cache@v4
         with: