modulegroups: dynamically select tone-mapper defaults in beginner preset (fixes #20959)

[Mr-Charvaka]

Resolves #20959.

Purpose & Goal

Ensure the beginner preset in Quick Access Panel (QAP) respects active user workflow preferences (filmicrgb, agx, or sigmoid) rather than always hardcoding sigmoid.

Implementation Details

• Updated the preset initialization logic in src/libs/modulegroups.c to inspect the workflow configuration (plugins/darkroom/workflow).
• Conditionally load filmicrgb, agx, or sigmoid based on active workflow settings.

Testing & Verification Approach

• Verified the beginner panel configuration dynamically maps the correct modules:
  • filmic workflow -> filmicrgb
  • AgX workflow -> agx
  • sigmoid or none -> sigmoid

Regression Safety

Maintains safe fallback behavior and respects existing scene-referred configuration schemes without breaking legacy presets.

Development Note

This pull request was prepared with AI-assisted pair-programming (using the Gemini-powered Antigravity agent), and has been manually reviewed and refined for correctness.

[wpferguson]

If this PR was generated with AI assistance, please note that.

What kind of testing was done? Was it only tested to make sure the problem was fixed or was testing also done to make sure there were no regressions or issues created by the fix?

[Mr-Charvaka]

@wpferguson I have updated the PR you can find the specific testing approach, regression safety checks, and implementation breakdown posted directly in the Pull Request description at the top of this page.

[TurboGit]

The goal here was to always use sigmoid for beginner workflow as this is the simplest tone mapper.