chore(ci): enable Gradle dependency caching across GitHub workflows

[Ludy87]

Description of Changes

This pull request updates the CI/CD workflows and Gradle configuration to improve build reproducibility, security, and external dependency management. The main changes include standardizing Gradle setup across workflows, securely injecting Maven credentials, and enabling Gradle build caching. There are also minor improvements to dependency version management and plugin repository configuration.

CI/CD Workflow Improvements:

• Standardized Gradle setup across all GitHub Actions workflows by explicitly adding a Setup Gradle step using gradle/actions/setup-gradle@v5.0.0 and specifying Gradle version 8.14. This replaces previous usages and ensures consistency. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

• Enabled Gradle build cache (--build-cache) for all build-related commands in workflows, improving build performance and consistency. Also removed unnecessary clean commands before builds to further optimize workflow times. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Security and Dependency Management:

• Injected Maven credentials (MAVEN_USER, MAVEN_PASSWORD, MAVEN_PUBLIC_URL) as environment variables in all relevant workflow steps, supporting secure access to private or custom Maven repositories. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

• Added a pluginManagement block in settings.gradle to allow Gradle plugins to be resolved from a custom Maven repository if specified by environment variables, increasing flexibility for plugin sourcing.

Build and Dependency Versioning:

• Updated app/proprietary/build.gradle to use the bouncycastleVersion variable for the Bouncy Castle dependency version, improving maintainability and consistency of dependency versioning.

Workflow Trigger Improvements:

• Expanded the file path triggers in .github/workflows/sync_files_v2.yml to include additional Gradle build files, ensuring the workflow runs when any core build files are changed.

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Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (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 (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

Translations (if applicable)

• I ran scripts/counter_translation.py

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 for more details.

[Copilot]

Pull request overview

This PR adds Gradle dependency caching to GitHub Actions workflows to improve CI build performance by reusing previously built dependencies and outputs across workflow runs.

Key changes:

• Added cache: "gradle" to all actions/setup-java steps across 10 workflow files
• Updated Java version from "17" to "21" in PR-Demo-Comment-with-react.yml to align with other workflows

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
.github/workflows/build.yml	Added Gradle caching to 5 different jobs (build-variants, openapi-docs, licenses, docker-build, gradle-wrapper-validation)
.github/workflows/PR-Demo-Comment-with-react.yml	Added Gradle caching and corrected Java version from 17 to 21 in deploy-pr job
.github/workflows/frontend-backend-licenses-update.yml	Added Gradle caching to backend-licenses job
.github/workflows/multiOSReleases.yml	Added Gradle caching to all 3 platform-specific jobs (linux, windows, macos)
.github/workflows/pre_commit.yml	Added Gradle caching to pre-commit build job
.github/workflows/push-docker-v2.yml	Added Gradle caching to push job
.github/workflows/push-docker.yml	Added Gradle caching to push job
.github/workflows/swagger.yml	Added Gradle caching to generate job
.github/workflows/tauri-build.yml	Added Gradle caching to build-tauri job
.github/workflows/testdriver.yml	Added Gradle caching to deploy job

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[stirlingbot]

✅ Frontend License Check Passed

All frontend licenses have been validated and no compatibility warnings were detected.

The frontend license report has been updated successfully.

[stirlingbot]

✅ Backend License Check Passed

All backend dependencies have valid and allowed licenses.

The backend license report has been updated successfully.