Deprecate flowchart-level htmlLabels config option

[darshanr0107]

📑 Summary

• Mermaid had two configs for HTML labels (htmlLabels and flowchart.htmlLabels) with inconsistent precedence.
• This PR deprecates flowchart.htmlLabels. Root-level htmlLabels is now the single source of truth.

📏 Design Decisions

• AddedgetEffectiveHtmlLabels(config) to centralize logic.
• Root-level takes precedence;flowchart.htmlLabels logs a deprecation warning.
• Marked flowchart.htmlLabelsas deprecated in the schema.

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added necessary unit/e2e tests.
• 📓 have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features.
• 🦋 If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

[changeset-bot]

🦋 Changeset detected

Latest commit: e82e464

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
mermaid	Minor

Not sure what this means? Click here to learn what changesets are.

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commit: e82e464

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Build	Status	Details	Updated (UTC)
default (Inspect)	⚠️ Changes detected (Review)	145 changed	Sep 25, 2025, 12:14 PM

[codecov]

Codecov Report

❌ Patch coverage is 11.59420% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 3.59%. Comparing base (d5c4eff) to head (e82e464).
⚠️ Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/mermaid/src/dagre-wrapper/nodes.js	0.00%	10 Missing ⚠️
...ackages/mermaid/src/diagrams/requirement/styles.js	0.00%	9 Missing ⚠️
.../src/rendering-util/rendering-elements/clusters.js	0.00%	7 Missing ⚠️
packages/mermaid/src/dagre-wrapper/clusters.js	0.00%	5 Missing ⚠️
packages/mermaid/src/dagre-wrapper/edges.js	0.00%	4 Missing ⚠️
packages/mermaid/src/dagre-wrapper/shapes/util.js	0.00%	4 Missing ⚠️
packages/mermaid/src/dagre-wrapper/createLabel.js	0.00%	3 Missing ⚠️
...aid/src/rendering-util/rendering-elements/edges.js	0.00%	3 Missing ⚠️
...c/rendering-util/rendering-elements/shapes/util.ts	0.00%	3 Missing ⚠️
packages/mermaid/src/config.ts	75.00%	2 Missing ⚠️
... and 6 more

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #6995      +/-   ##
==========================================
+ Coverage     3.57%   3.59%   +0.01%     
==========================================
  Files          473     474       +1     
  Lines        47139   47177      +38     
  Branches       730     732       +2     
==========================================
+ Hits          1687    1694       +7     
- Misses       45452   45483      +31     

Flag	Coverage Δ
unit	3.59% <11.59%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/mermaid/src/config.type.ts	100.00% <ø> (ø)
packages/mermaid/src/diagrams/common/common.ts	32.05% <100.00%> (+0.29%)	⬆️
.../mermaid/src/diagrams/requirement/requirementDb.ts	0.00% <0.00%> (ø)
packages/mermaid/src/config.ts	25.17% <75.00%> (+3.04%)	⬆️
packages/mermaid/src/dagre-wrapper/shapes/note.js	0.00% <0.00%> (ø)
...ges/mermaid/src/diagrams/class/classRenderer-v2.ts	0.37% <0.00%> (-0.01%)	⬇️
packages/mermaid/src/mermaidAPI.ts	0.30% <0.00%> (-0.01%)	⬇️
...c/rendering-util/rendering-elements/createLabel.js	0.00% <0.00%> (ø)
...c/rendering-util/rendering-elements/shapes/note.ts	0.00% <0.00%> (ø)
packages/mermaid/src/dagre-wrapper/createLabel.js	0.00% <0.00%> (ø)
... and 8 more

... and 1 file with indirect coverage changes

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