Fix CI: remove Docker-in-Docker, install Stack directly

The ./hs Docker wrapper runs docker inside the Gitea runner container.
Since project paths inside the runner container don't exist on the Docker
host, the volume mount creates an empty /work directory, and Stack finds
no packages (error S-8506).

Fix: install Stack directly via get.haskellstack.org, use STACK_ROOT for
caching, and build with stack directly (no Docker-in-Docker).

Also add symlink for gitea-actions.sh convenience script.

.gitea/workflows/build.yml

@@ -9,24 +9,26 @@ jobs:
   build:
     runs-on: ubuntu-latest
     env:
-      CONVERGE_HASKELL_TOOLS_IMAGE: ghcr.io/flipstone/haskell-tools:debian-ghc-9.10.3-5d6640d
+      STACK_ROOT: .stack-root
     steps:
       - name: Checkout
         uses: actions/checkout@v4
-        with:
-          path: .
+
+      - name: Install Stack
+        run: |
+          curl -sSL https://get.haskellstack.org/ | sh
 
       - name: Cache Stack
         uses: actions/cache@v4
         with:
           path: .stack-root
-          key: stack-${{ runner.os }}-${{ hashFiles('stack.yaml', 'package.yaml') }}
-          restore-keys: stack-${{ runner.os }}-
+          key: stack-v2-${{ runner.os }}-${{ hashFiles('stack.yaml', 'package.yaml') }}
+          restore-keys: stack-v2-${{ runner.os }}-
 
       - name: Build
         run: |
-          mkdir -p .stack-root build
-          ./hs stack build --copy-bins --local-bin-path /work/build
+          mkdir -p build
+          stack build --copy-bins --local-bin-path ./build
 
       - name: Compress with UPX
         run: |

scripts/gitea-actions.sh

@@ -0,0 +1 @@
+../.pi/skills/gitea-actions/scripts/gitea-actions.sh