[shiv07-blip]

What kind of change does this PR introduce?

Bugfix - corrects an early-return check in JsonEditor that mishandled a code block found at index 0.

Issue Number:
Closes #1920

Screenshots/videos:

N/A - this is a logic-level fix with no visible UI change. The behaviour is covered by a new Cypress component test.

If relevant, did you update the documentation?

Not needed - no public API or docs behaviour changed.

Summary
The JsonEditor uses indexOf to locate the code block inside the markdown. That returns 0 when the block is at the start, and the old check if (!positionOfCodeInFullMarkdown) treated 0 as "not found", so the block was never handled. I replaced it with an explicit check for undefined and -1.
I also added a test in cypress/components/JsonEditor.cy.tsx that places the code block at index 0 and checks that the caption does not get the mb-10 class.
Tested with yarn lint, yarn typecheck, and the JsonEditor Cypress spec (39 passing).

Does this PR introduce a breaking change?

no

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5158a0a) to head (ea0d6fd).
⚠️ Report is 39 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #2640   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           31        31           
  Lines          695       737   +42     
  Branches       215       229   +14     
=========================================
+ Hits           695       737   +42     

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