Fix edge labels for ER and requirement diagrams when config.flowchart.htmlLabels is false

[darshanr0107]

📑 Summary

This PR fixes edge label rendering issues in ER and requirement diagrams when flowchart.htmlLabels is set to false.

Note: This PR should be merged before #6995

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Latest commit: aac86f7

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commit: aac86f7

[codecov]

Codecov Report

❌ Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.57%. Comparing base (d5bc07d) to head (aac86f7).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ackages/mermaid/src/diagrams/requirement/styles.js	0.00%	9 Missing ⚠️
packages/mermaid/src/diagrams/er/styles.ts	0.00%	3 Missing ⚠️
.../mermaid/src/diagrams/requirement/requirementDb.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #7296      +/-   ##
==========================================
- Coverage     3.57%   3.57%   -0.01%     
==========================================
  Files          473     474       +1     
  Lines        47475   47498      +23     
  Branches       734     734              
==========================================
  Hits          1696    1696              
- Misses       45779   45802      +23     

Flag	Coverage Δ
unit	3.57% <0.00%> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
.../mermaid/src/diagrams/requirement/requirementDb.ts	0.00% <0.00%> (ø)
packages/mermaid/src/diagrams/er/styles.ts	0.00% <0.00%> (ø)
...ackages/mermaid/src/diagrams/requirement/styles.js	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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Build	Status	Details	Updated (UTC)
default (Inspect)	👍 Changes approved	58 changed, 4 added	Jan 6, 2026, 2:37 PM

[aloisklink]

LGTM!

@darshanr0107, can you maybe add a before and after screenshot to the PR description? After that, I think it's good to merge.