Add frozen: 'start' | 'end' for end-edge column pinning

[PaloSP]

Adds right-edge column pinning — long-standing ask (#2873, #3671).

• Column.frozen widens to boolean | 'start' | 'end'. true stays an alias for 'start' (backwards compatible).
• 'end' pins to the inline-end edge; symmetric infra: --rdg-frozen-end-${idx} CSS var, rdg-cell-frozen-end class, end-shadow + top/bottom-summary variants, logical properties throughout.

Credit to @robert-luoqing for #3671 which informed the approach. API per @amanmahajan7 and @nstepien's 'start' | 'end' refinement.

One check: "we want to prevent the shadow logic" (#3671 2026-04-21) — I interpreted as "preserve" and mirrored the start-shadow symmetrically. If the intent was otherwise, happy to drop it.

Tests: new test/browser/column/frozenEnd.test.ts + additions to virtualization.test.ts and direction.test.ts. Demo updated in CommonFeatures.

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.54%. Comparing base (c204e91) to head (5016075).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4034      +/-   ##
==========================================
+ Coverage   97.49%   97.54%   +0.05%     
==========================================
  Files          38       38              
  Lines        1516     1548      +32     
  Branches      486      499      +13     
==========================================
+ Hits         1478     1510      +32     
  Misses         38       38              

Files with missing lines	Coverage Δ
src/DataGrid.tsx	98.86% <100.00%> (+0.01%)	⬆️
src/GroupRow.tsx	100.00% <ø> (ø)
src/hooks/useCalculatedColumns.ts	100.00% <100.00%> (ø)
src/hooks/useViewportColumns.ts	100.00% <100.00%> (ø)
src/utils/activePositionUtils.ts	98.92% <100.00%> (ø)
src/utils/colSpanUtils.ts	100.00% <100.00%> (ø)
src/utils/index.ts	92.30% <100.00%> (+1.39%)	⬆️
src/utils/styleUtils.ts	100.00% <100.00%> (ø)

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[amanmahajan7]

Thank you for the PR. A few quick comments. I can do a detailed review in 2 weeks (on a vacation)

[amanmahajan7]

Let's add a type and reuse it

[amanmahajan7]

We can reuse the cellFrozen class

[amanmahajan7]

Let's extract the common styles in frozenColumnShadowClassname and we can add frozenColumnShadowStart/EndClassname

[amanmahajan7]

We should rename it to be consistent

Suggested change

	import { cellFrozen, cellFrozenEnd } from './cell';
	import { cellFrozenStart, cellFrozenEnd } from './cell';

[amanmahajan7]

same here, let's dedupe

& > .${cellFrozen}:first-child::before,
& > .${cellFrozenEnd}:last-child::after { }

& > .${cellFrozen}:first-child::before { }

& > .${cellFrozenEnd}:last-child::after { }

[PaloSP]

@amanmahajan7 pushed a revision addressing all 5 comments.

On comment 4: intentional divergence from the literal suggestion. Comment 2's dedup removed the separate cellFrozenEnd export, so row.ts no longer imports from ./cell at all — its selectors use the DOM marker classes (.rdg-cell-frozen / .rdg-cell-frozen-end) directly. cellFrozen kept as the shared identifier per your phrasing in #2. Happy to rename cellFrozen → cellFrozenStart and restore an import if you prefer.

Two open questions, both breaking — your call:

1. Rename CSS var --rdg-frozen-left-${idx} → --rdg-frozen-start-${idx} for symmetry with new --rdg-frozen-end-${idx}?
2. Rename DOM marker .rdg-cell-frozen → .rdg-cell-frozen-start for symmetry with new .rdg-cell-frozen-end?

Both currently kept as-is (non-breaking). No rush — enjoy the vacation.