fix(prd-1): skip actor check on Forgejo + replace setup-bun with curl install

- Skip checkHumanActor on Forgejo (no bot accounts, avoids read:user scope)
- Replace oven-sh/setup-bun action with curl install in action.yml
  (Forgejo runner pre-fetches all uses: refs even when if: skips them)
- Mirror oven-sh/setup-bun created at xternal/setup-bun for future use

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

action.yml

@@ -182,15 +182,12 @@ runs:
         echo "platform=${DETECTED}" >> "$GITHUB_OUTPUT"
         echo "Detected platform: ${DETECTED}"
 
+    # NOTE: upstream uses oven-sh/setup-bun here, but Forgejo runners
+    # pre-fetch all `uses:` refs even when `if:` would skip them, causing
+    # failures. The curl install works on both platforms and avoids the
+    # external action dependency. When merging upstream, keep this block.
     - name: Install Bun
-      if: inputs.path_to_bun_executable == '' && steps.detect-platform.outputs.platform != 'forgejo'
-      uses: oven-sh/setup-bun@3d267786b128fe76c2f16a390aa2448b815359f3 # https://github.com/oven-sh/setup-bun/releases/tag/v2.1.2
-      with:
-        bun-version: 1.3.6
-        token: ${{ inputs.github_token || github.token }}
-
-    - name: Install Bun (Forgejo)
-      if: inputs.path_to_bun_executable == '' && steps.detect-platform.outputs.platform == 'forgejo'
+      if: inputs.path_to_bun_executable == ''
       shell: bash
       run: |
         if command -v bun &> /dev/null; then