Fix silent curl failures in desktop-lite feature installation

[Copilot]

The desktop-lite feature was failing during installation because curl downloads were silently failing on HTTP errors, creating corrupted zip files that caused unzip to fail with "End-of-central-directory signature not found."

Changes

• Added -f flag to curl commands to return non-zero exit codes on HTTP errors (4xx/5xx)
• Added explicit error handling with early exit for failed downloads:
  • Cascadia Code fonts download
  • noVNC archive download
  • websockify archive download
• Incremented feature version to 1.3.1

Example

# Before: silently creates corrupted file on HTTP error
curl -sSL <url> -o /tmp/file.zip
unzip /tmp/file.zip  # fails with cryptic error

# After: fails fast with clear error message
if ! curl -fsSL <url> -o /tmp/file.zip; then
    echo "Failed to download <resource>"
    exit 1
fi

This prevents downstream failures from corrupted files when GitHub returns HTTP errors due to rate limiting or service issues.

Original prompt

Fix the failing GitHub Actions workflow test (desktop-lite, ubuntu:focal)
Analyze the workflow logs, identify the root cause of the failure, and implement a fix.
Job ID: 63256089501
Job URL: https://github.com/devcontainers/features/actions/runs/21908693416/job/63256089501

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