feat(common): add automatic height for multiline column headers

[ghiscoding]

replicate SlickGrid PR 6pac/SlickGrid#1282

Summary

Adds opt-in automatic header-height calculation for multiline column headers across SlickGrid Universal.

Why

Multiline headers could be clipped at the default fixed height. This allows headers to expand to fit their rendered content while keeping the feature disabled by default for backward compatibility.

Changes

• Added the autoHeaderHeight grid option.
• Measures rendered header content and synchronizes frozen header panes.
• Recalculates after column resizing, autosizing, and column updates.
• Supports multiline text, HTML, and DOM-based header content.
• Prevented Material theme spacing from inflating calculated heights.
• Updated Vanilla, Angular, Aurelia, React, and Vue demos.
• Added Cypress coverage for wrapped headers.
• Added unit coverage for calculation, frozen panes, toggling, and recalculation.
• Updated styling documentation and repository testing instructions.

Validation

• 451 SlickGrid unit tests pass.
• Coverage checks pass for the changed behavior.
• Package build and Sass build pass.
• Lint and Prettier checks pass.
• Cypress suites pass in the running Cypress UI/watch-server workflow.

Comments

This change spans the common package, framework demos, tests, and documentation because the shared grid behavior must be demonstrated and validated consistently across all supported frameworks.

AI / LLM assistance

• AI / LLM assistance used:
  • No
  • Yes
• If Yes:
  • which tool/model: Codex, GPT-5.6 Terra
  • how was it used: Implemented the feature, updated framework demos/tests/documentation, diagnosed regressions, and assisted with validation.

Checklist

• The changes are limited to only one scope (shared behavior plus corresponding framework demos/docs; see Comments).
• Tests were added or updated where appropriate.
• Documentation was updated where appropriate.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.0%. Comparing base (33bfbb1) to head (aa48839).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2780   +/-   ##
=======================================
  Coverage   100.0%   100.0%           
=======================================
  Files         199      199           
  Lines       25776    25812   +36     
  Branches     9132     9142   +10     
=======================================
+ Hits        25776    25812   +36     

Flag	Coverage Δ
angular	100.0% <ø> (ø)
universal	100.0% <100.0%> (ø)

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commit: aa48839