ci(docker,workflow): install bash in images, keep /bin/sh POSIX, and simplify PR test-build deps (#4879)

# Description of Changes

This pull request updates the Docker setup for all image variants
(`Dockerfile`, `Dockerfile.fat`, and `Dockerfile.ultra-lite`) to improve
shell compatibility and ensure consistent behavior across environments.
The most important changes are grouped below:

Shell compatibility improvements:

* Added installation of `bash` and created a symlink from `/bin/bash` to
`/bin/sh` to ensure scripts expecting `bash` work correctly in all
Docker images. (`Dockerfile`:
[[1]](diffhunk://#diff-dd2c0eb6ea5cfc6c4bd4eac30934e2d5746747af48fef6da689e85b752f39557L42-R44)
`Dockerfile.fat`:
[[2]](diffhunk://#diff-571631582b988e88c52c86960cc083b0b8fa63cf88f056f26e9e684195221c27L56-R58)
`Dockerfile.ultra-lite`:
[[3]](diffhunk://#diff-ebe2e5849a198a8b5be70f42dcd1ddc518c7584d525f6492d221db9f7a45a6f5L27-R29)

Default shell consistency:

* Added a symlink from `/bin/busybox` to `/bin/sh` after setting user
permissions to ensure the default shell remains available and consistent
for system utilities. (`Dockerfile`:
[[1]](diffhunk://#diff-dd2c0eb6ea5cfc6c4bd4eac30934e2d5746747af48fef6da689e85b752f39557L101-R104)
`Dockerfile.fat`:
[[2]](diffhunk://#diff-571631582b988e88c52c86960cc083b0b8fa63cf88f056f26e9e684195221c27L114-R117)
`Dockerfile.ultra-lite`:
[[3]](diffhunk://#diff-ebe2e5849a198a8b5be70f42dcd1ddc518c7584d525f6492d221db9f7a45a6f5L47-R50)

---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

.github/workflows/build.yml

@@ -266,7 +266,7 @@ jobs:
 
   test-build-docker-images:
     if: github.event_name == 'pull_request' && needs.files-changed.outputs.project == 'true'
-    needs: [files-changed, build, check-generateOpenApiDocs, check-licence]
+    needs: [files-changed, build]
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false

Dockerfile

@@ -39,7 +39,9 @@ ENV DISABLE_ADDITIONAL_FEATURES=true \
     TMP=/tmp/stirling-pdf
 
 # JDK for app
-RUN printf '%s\n' \
+RUN apk add --no-cache bash \
+    && ln -sf /bin/bash /bin/sh \
+    && printf '%s\n' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/main' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/community' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/testing' \
@@ -98,7 +100,8 @@ RUN printf '%s\n' \
     # User permissions
     addgroup -S stirlingpdfgroup && adduser -S stirlingpdfuser -G stirlingpdfgroup && \
     chown -R stirlingpdfuser:stirlingpdfgroup $HOME /scripts /usr/share/fonts/opentype/noto /configs /customFiles /pipeline /tmp/stirling-pdf && \
-    chown stirlingpdfuser:stirlingpdfgroup /app.jar
+    chown stirlingpdfuser:stirlingpdfgroup /app.jar && \
+    ln -sf /bin/busybox /bin/sh
 
 EXPOSE 8080/tcp
 

Dockerfile.fat

@@ -53,7 +53,9 @@ ENV DISABLE_ADDITIONAL_FEATURES=true \
     TMP=/tmp/stirling-pdf
 
 # JDK for app
-RUN printf '%s\n' \
+RUN apk add --no-cache bash \
+    && ln -sf /bin/bash /bin/sh \
+    && printf '%s\n' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/main' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/community' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/testing' \
@@ -111,7 +113,8 @@ RUN printf '%s\n' \
     # User permissions
     addgroup -S stirlingpdfgroup && adduser -S stirlingpdfuser -G stirlingpdfgroup && \
     chown -R stirlingpdfuser:stirlingpdfgroup $HOME /scripts /usr/share/fonts/opentype/noto /configs /customFiles /pipeline /tmp/stirling-pdf && \
-    chown stirlingpdfuser:stirlingpdfgroup /app.jar
+    chown stirlingpdfuser:stirlingpdfgroup /app.jar && \
+    ln -sf /bin/busybox /bin/sh
 
 EXPOSE 8080/tcp
 # Set user and run command

Dockerfile.ultra-lite

@@ -24,7 +24,9 @@ COPY scripts/installFonts.sh /scripts/installFonts.sh
 COPY app/core/build/libs/*.jar app.jar
 
 # Set up necessary directories and permissions
-RUN printf '%s\n' \
+RUN apk add --no-cache bash \
+    && ln -sf /bin/bash /bin/sh \
+    && printf '%s\n' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/main' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/community' \
       'https://dl-cdn.alpinelinux.org/alpine/edge/testing' \
@@ -44,7 +46,8 @@ RUN printf '%s\n' \
     chmod +x /scripts/*.sh && \
     addgroup -S stirlingpdfgroup && adduser -S stirlingpdfuser -G stirlingpdfgroup && \
     chown -R stirlingpdfuser:stirlingpdfgroup $HOME /scripts /pipeline /configs /customFiles /tmp/stirling-pdf && \
-    chown stirlingpdfuser:stirlingpdfgroup /app.jar
+    chown stirlingpdfuser:stirlingpdfgroup /app.jar && \
+    ln -sf /bin/busybox /bin/sh
 
 # Set environment variables
 ENV ENDPOINTS_GROUPS_TO_REMOVE=CLI