feat: MUI 4 to BUI migration - replace Accordion with BUI Accordion

[schultzp2020]

Summary

Add a codemod that migrates the common MUI Accordion / AccordionSummary / AccordionDetails structure to the BUI accordion API.

This family appears often enough in the migration tracker that it is worth a dedicated issue, even though some real-world cases will still need TODO markers for custom summary markup or controlled state.

Detection Criteria

• Accordion, AccordionSummary, and AccordionDetails imports from @material-ui/core
• plain summary text or summary text wrapped in a simple Typography node
• optional expandIcon props on AccordionSummary

Transformation Logic

1. Replace the MUI accordion imports with Accordion, AccordionTrigger, and AccordionPanel from @backstage/ui.
2. Map simple summary text to the title prop on AccordionTrigger.
3. Move AccordionDetails children into AccordionPanel.
4. Drop or TODO-mark custom expandIcon props when the BUI destination pattern no longer needs them.
5. Insert TODO(backstage-codemod): finish accordion migration manually for controlled accordions, heavily custom summary markup, or nested interactive content that changes the trigger semantics.

Before / After Example

Simple accordion:

// Before
<Accordion>
  <AccordionSummary expandIcon={<ExpandMoreIcon />}>
    Section title
  </AccordionSummary>
  <AccordionDetails>Body</AccordionDetails>
</Accordion>

// After
<Accordion>
  <AccordionTrigger title="Section title" />
  <AccordionPanel>Body</AccordionPanel>
</Accordion>

Notes / Edge Cases

• Do not auto-collapse multiple accordions into AccordionGroup unless the parent grouping semantics are explicit.
• This issue is separate from the older Backstage Collapsible -> Accordion codemod because the source API here is MUI, not @backstage/ui.
• Keep custom expansion state logic explicit and marked for review rather than guessing a new state model.
• The migration skill and the tracker counts are the primary sources of truth for this family.

Changeset (when implementing)

• Package: @backstage/migrate-mui-accordion-to-bui-accordion
• Bump: minor (initial release)
• Summary example: Add codemod to migrate mui accordion to bui accordion for the Backstage MUI 4 to BUI migration

Implementation notes

• Target directory: codemods/misc/migrate-mui-accordion-to-bui-accordion/
• Branch/worktree: .worktrees/feat/mui4-to-bui/migrate-mui-accordion-to-bui-accordion
• Open PR when ready; one PR per codemod