ci(maestro): drop container, install rustup + tmux on default image

`rust:1.83-bookworm` has no Node, which breaks `actions/checkout@v4`
(it's a JS action). The default gitea runner image has Node, so go back
to that and install rustup + tmux + git + build-essential ourselves.

.gitea/workflows/ci.yml

@@ -10,18 +10,21 @@ on:
 jobs:
   rust:
     runs-on: ubuntu-latest
-    container:
-      image: rust:1.83-bookworm
     steps:
       - uses: actions/checkout@v4
 
-      - name: Install runtime test deps (tmux + git)
+      - name: Install tmux + build deps
         run: |
           apt-get update
-          apt-get install -y --no-install-recommends tmux git ca-certificates
+          apt-get install -y --no-install-recommends \
+            tmux git curl ca-certificates build-essential pkg-config
 
-      - name: Add rustfmt + clippy
-        run: rustup component add rustfmt clippy
+      - name: Install rustup + stable toolchain
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
+            | sh -s -- -y --profile minimal --default-toolchain stable \
+                       --component rustfmt --component clippy
+          echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
 
       - name: Cache cargo
         uses: actions/cache@v4