fix - install unzip and extend setup-bun to handle ARM64 Blacksmith runners

Blacksmith's ubuntu-2404 runners run on ARM64 hardware (RUNNER_ARCH=ARM64).
The previous action only built an explicit bun download URL for X64, so ARM64
fell through to oven-sh/setup-bun@v2's default path which downloads
bun-linux-aarch64.zip and extracts it via the system unzip command. Blacksmith's
ARM64 Ubuntu image doesn't pre-install unzip, causing all e2e and unit CI jobs
to fail at the Setup Bun step.

Two changes:
- Add a Linux step that installs unzip if not already present (direct fix)
- Rewrite the URL construction with case/esac covering both X64 and ARM64 for
  all OS variants, replacing the x64-only if block (architecture fix)

Author: lgarceau768

.github/actions/setup-bun/action.yml

@@ -3,19 +3,30 @@ description: "Setup Bun with caching and install dependencies"
 runs:
   using: "composite"
   steps:
-    - name: Get baseline download URL
+    - name: Ensure unzip is available
+      if: runner.os == 'Linux'
+      shell: bash
+      # oven-sh/setup-bun extracts the downloaded zip via the system `unzip` command
+      # on Linux. Blacksmith's ARM64 ubuntu-2404 runners don't pre-install it.
+      run: command -v unzip >/dev/null 2>&1 || sudo apt-get install -y --no-install-recommends unzip
+
+    - name: Get bun download URL
       id: bun-url
       shell: bash
       run: |
-        if [ "$RUNNER_ARCH" = "X64" ]; then
-          V=$(node -p "require('./package.json').packageManager.split('@')[1]")
-          case "$RUNNER_OS" in
-            macOS)   OS=darwin ;;
-            Linux)   OS=linux ;;
-            Windows) OS=windows ;;
-          esac
-          echo "url=https://github.com/oven-sh/bun/releases/download/bun-v${V}/bun-${OS}-x64-baseline.zip" >> "$GITHUB_OUTPUT"
-        fi
+        V=$(node -p "require('./package.json').packageManager.split('@')[1]")
+        case "$RUNNER_OS" in
+          macOS)   OS=darwin  ;;
+          Linux)   OS=linux   ;;
+          Windows) OS=windows ;;
+          *) exit 0 ;;
+        esac
+        case "$RUNNER_ARCH" in
+          X64)   ARCH=x64-baseline ;;
+          ARM64) ARCH=aarch64      ;;
+          *) exit 0 ;;
+        esac
+        echo "url=https://github.com/oven-sh/bun/releases/download/bun-v${V}/bun-${OS}-${ARCH}.zip" >> "$GITHUB_OUTPUT"
 
     - name: Setup Bun
       uses: oven-sh/setup-bun@v2