Devcontainer (#3097)

# Description of Changes

Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)

---

## 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/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/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/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### 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/DeveloperGuide.md#6-testing)
for more details.

Dockerfile.dev

@@ -0,0 +1,56 @@
+# dockerfile.dev
+
+# Basisimage: Gradle mit JDK 17 (Debian-basiert)
+FROM gradle:8.12-jdk17
+
+# Als Root-Benutzer arbeiten, um benötigte Pakete zu installieren
+USER root
+
+# Update und Installation zusätzlicher Pakete (Debian/Ubuntu-basiert)
+RUN apt-get update && apt-get install -y \
+  wget \
+  ca-certificates \
+  tzdata \
+  tini \
+  bash \
+  curl \
+  libreoffice \
+  poppler-utils \
+  qpdf \
+  tesseract-ocr \
+  tesseract-ocr-eng \
+  fonts-dejavu \
+  fonts-noto \
+  python3 \
+  python3-pip \
+  python3-venv \
+  && apt-get clean && rm -rf /var/lib/apt/lists/*
+
+# Setze die Environment Variable für setuptools
+ENV SETUPTOOLS_USE_DISTUTILS=local
+
+# Installation der benötigten Python-Pakete
+RUN python3 -m venv /opt/venv \
+  && . /opt/venv/bin/activate \
+  && pip install --upgrade setuptools \
+  && pip install --no-cache-dir WeasyPrint pdf2image pillow unoserver opencv-python-headless pre-commit
+
+# Füge den venv-Pfad zur globalen PATH-Variable hinzu, damit die Tools verfügbar sind
+ENV PATH="/opt/venv/bin:$PATH"
+
+# Erstelle notwendige Verzeichnisse und lege einen Nicht‑Root Benutzer an
+RUN mkdir -p /home/devuser/{configs,logs,customFiles,pipeline/watchedFolders,pipeline/finishedFolders} \
+  && adduser --disabled-password --gecos '' devuser \
+  && chown -R devuser:devuser /home/devuser
+
+RUN mkdir -p /home/devuser/logs && chown devuser:devuser /home/devuser/logs
+RUN mkdir -p /workspace/logs && chown devuser:devuser /workspace/logs
+RUN mkdir -p /workspace/src && chown devuser:devuser /workspace/src
+RUN mkdir -p /workspace/src/main && chown devuser:devuser /workspace/src/main
+RUN mkdir -p /workspace/src/main/resources && chown devuser:devuser /workspace/src/main/resources
+
+# Setze das Arbeitsverzeichnis (wird später per Bind-Mount überschrieben)
+WORKDIR /workspace
+
+# Wechsel zum Nicht‑Root Benutzer
+USER devuser