Support multiple customized preview styles

[koppor]

⚠️ This issue takes time and NOT a one-shot LLM prompt - you need to 🧠 ⚠️

Currently JabRef allows exactly one customized preview style alongside a fixed list of [CSL preview styles](https://docs.jabref.org/setup/preview). The customized style uses the [custom export filter syntax](https://docs.jabref.org/collaborative-work/export/customexports).

Wish: Allow users to create and manage multiple customized preview styles.

Changes required:

1. Preference UI — "Available" panel: Split into two tabs: "CSL" and "Customized"
2. Customized preview editor: Show the editor below the lists whenever a customized style is selected (either in "Available" or in the active list on the right)
3. Naming: Allow each customized style to be named
4. Preferences: Update storage to support multiple customized styles, including migration of existing single-style preferences and tests

Documentation to update:

• [Entry preview setup](https://docs.jabref.org/setup/preview) → [source](https://github.com/JabRef/user-documentation/blob/main/en/setup/preview.md)
• [Custom export filters](https://docs.jabref.org/collaborative-work/export/customexports) (if syntax/preference structure is referenced) → [source](https://github.com/JabRef/user-documentation/blob/main/en/collaborative-work/export/customexports.md)

Related code:

• Preview preferences: org.jabref.logic.preview.PreviewPreferences
• Preferences UI: org.jabref.gui.preferences.preview (PreviewTab, PreviewTabViewModel)

[thesauravpoddar]

I would like to work on it

[thesauravpoddar]

/assign-me

[subhramit]

@thesauravpoddar you have consecutively assigned yourself to four issues without submitting a PR for the first, second, third or fourth.
Please note that hogging issues for the sake of blocking them is not the right conduct in open-source projects, but progressively taking up work as you finish existing assignments is.
Un-assigning you from the rest of the issues.

cc @koppor should we gate our assignment limit based on good xth issues instead of just good firsts?

[thesauravpoddar]

@thesauravpoddar you have consecutively assigned yourself to four issues without submitting a PR for the first, second, third or fourth.
Please note that hogging issues for the sake of blocking them is not the right conduct in open-source projects, but progressively taking up work as you finish existing assignments is.
Un-assigning you from the rest of the issues.

cc @koppor should we gate our assignment limit based on good xth issues instead of just good firsts?

Okay understood and i am working on pr of those issues

[koppor]

Okay understood and i am working on pr of those issues

And please use 🧠 for that.

[santhosh290605]

hi there , i would like to work on it

[dvinit]

can I work on this one?

[Al-Zaytoun]

/assign-me