Adds automated job to check for broken links in documentation and fixes some links (#3888)

# Description

Broken links often creep into the documentation without anyone noticing.
This adds an automated job to check through links referenced in the docs
and readmes to find any broken or outdated links.

Additionally, fixes a few broken links that were discovered by the job.

## Type of change

- Documentation update


## Checklist

- [x] I have read and understood the [contribution
guidelines](https://isaac-sim.github.io/IsaacLab/main/source/refs/contributing.html)
- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
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Author: kellyguo11

.github/ISSUE_TEMPLATE/question.md

@@ -10,4 +10,4 @@ Basic questions, related to robot learning, that are not bugs or feature request
 
 Advanced/nontrivial questions, especially in areas where documentation is lacking, are very much welcome.
 
-For questions that are related to running and understanding Isaac Sim, please post them at the official [Isaac Sim forums](https://docs.omniverse.nvidia.com/app_isaacsim/app_isaacsim/isaac_sim_forums.html).
+For questions that are related to running and understanding Isaac Sim, please post them at the official [Isaac Sim forums](https://forums.developer.nvidia.com/c/omniverse/simulation/69).

.github/workflows/check-links.yml

@@ -0,0 +1,120 @@
+# Copyright (c) 2022-2025, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
+# All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+name: Check Documentation Links
+
+on:
+  # Run on pull requests that modify documentation
+  pull_request:
+    paths:
+      - 'docs/**'
+      - '**.md'
+      - '.github/workflows/check-links.yml'
+  # Run on pushes to main branches
+  push:
+    branches:
+      - main
+      - devel
+      - 'release/**'
+    paths:
+      - 'docs/**'
+      - '**.md'
+      - '.github/workflows/check-links.yml'
+  # Allow manual trigger
+  workflow_dispatch:
+  # Run weekly to catch external links that break over time
+  schedule:
+    - cron: '0 0 * * 0'  # Every Sunday at midnight UTC
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  check-links:
+    name: Check for Broken Links
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - name: Restore lychee cache
+      uses: actions/cache@v4
+      with:
+        path: .lycheecache
+        key: cache-lychee-${{ github.sha }}
+        restore-keys: cache-lychee-
+
+    - name: Run Link Checker
+      uses: lycheeverse/lychee-action@v2
+      with:
+        # Check all markdown files and documentation
+        args: >-
+          --verbose
+          --no-progress
+          --cache
+          --max-cache-age 1d
+          --exclude-path './docs/_build'
+          --exclude-path './apps/warp-*'
+          --exclude-path './logs'
+          --exclude-path './outputs'
+          --exclude-loopback
+          --exclude '^file://'
+          --exclude '^mailto:'
+          --exclude 'localhost'
+          --exclude '127\.0\.0\.1'
+          --exclude 'example\.com'
+          --exclude 'your-organization'
+          --exclude 'YOUR_'
+          --exclude 'yourdomain'
+          --exclude 'user@'
+          --exclude 'helm\.ngc\.nvidia\.com'
+          --exclude 'slurm\.schedmd\.com'
+          --max-retries 3
+          --retry-wait-time 5
+          --timeout 30
+          --accept 200,201,202,203,204,206,301,302,303,307,308,429
+          --scheme https
+          --scheme http
+          '*.md'
+          '**/*.md'
+          'docs/**/*.rst'
+          'docs/**/*.html'
+        # Output results to a file
+        output: ./lychee-output.md
+        # Fail action on broken links
+        fail: true
+        # Optional: Use GitHub token for authenticated requests (higher rate limit)
+        token: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Print results to logs
+      if: always()
+      run: |
+        echo "========================================"
+        echo "Link Checker Results:"
+        echo "========================================"
+        if [ -f ./lychee-output.md ]; then
+          cat ./lychee-output.md
+          echo ""
+          echo "========================================"
+
+          # Also add to GitHub step summary for easy viewing
+          echo "## Link Checker Results" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          cat ./lychee-output.md >> $GITHUB_STEP_SUMMARY
+        else
+          echo "No output file generated"
+          echo "========================================"
+        fi
+
+    - name: Fail job if broken links found
+      if: failure()
+      run: |
+        echo "❌ Broken links were found in the documentation!"
+        echo "Please review the link checker report above and fix all broken links."
+        exit 1

README.md

@@ -87,7 +87,7 @@ innovation in robotics and simulation.
 Please see the [troubleshooting](https://isaac-sim.github.io/IsaacLab/main/source/refs/troubleshooting.html) section for
 common fixes or [submit an issue](https://github.com/isaac-sim/IsaacLab/issues).
 
-For issues related to Isaac Sim, we recommend checking its [documentation](https://docs.omniverse.nvidia.com/app_isaacsim/app_isaacsim/overview.html)
+For issues related to Isaac Sim, we recommend checking its [documentation](https://docs.isaacsim.omniverse.nvidia.com/latest/index.html)
 or opening a question on its [forums](https://forums.developer.nvidia.com/c/agx-autonomous-machines/isaac/67).
 
 ## Support

docs/source/deployment/cluster.rst

@@ -204,7 +204,7 @@ ANYmal rough terrain locomotion training can be executed with the following comm
 The above will, in addition, also render videos of the training progress and store them under ``isaaclab/logs`` directory.
 
 .. _Singularity: https://docs.sylabs.io/guides/2.6/user-guide/index.html
-.. _ETH Zurich Euler: https://scicomp.ethz.ch/wiki/Euler
+.. _ETH Zurich Euler: https://www.gdc-docs.ethz.ch/EulerManual/site/overview/
 .. _PBS Official Site: https://openpbs.org/
 .. _apptainer: https://apptainer.org/
 .. _documentation: https://www.apptainer.org/docs/admin/main/installation.html#install-ubuntu-packages