docs(cart-next): backfill jsdoc on functions and components

[filiphsps]

Summary

Adds JSDoc to all in-scope symbols in packages/cart/next per spec.

Counts

• Tier-1 symbols documented: 7
• Tier-2 symbols documented: 0
• Files touched: 4

Verification

• pnpm --filter @nordcom/cart-next typecheck passes
• pnpm --filter @nordcom/cart-next lint passes
• Rebased onto latest origin/master
• Diff is JSDoc-only (no logic changes)

[github-actions]

Coverage Report

Status	Category	Percentage	Covered / Total
🔵	Lines	82.35% (🎯 65%)	5528 / 6712
🔵	Statements	81.1% (🎯 60%)	6107 / 7530
🔵	Functions	81.53% (🎯 75%)	1523 / 1868
🔵	Branches	66.82% (🎯 50%)	3580 / 5357

File Coverage

File	Stmts	Branches	Functions	Lines	Uncovered Lines
Changed Files
packages/cart/next/src/cookie-storage.ts	100%	100%	100%	100%
packages/cart/next/src/form-actions.ts	47.56%	52.54%	41.17%	47.36%	41, 54-57, 72, 146-215, 220
packages/cart/next/src/typed-actions.ts	63.88%	42.85%	43.75%	61.76%	130, 161-172, 265-274

Generated in workflow #12874 for commit e8a5d49 by the Vitest Coverage Report Action

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.27%. Comparing base (e806f66) to head (e8a5d49).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1990   +/-   ##
=======================================
  Coverage   81.27%   81.27%           
=======================================
  Files         453      453           
  Lines        8427     8427           
  Branches     2693     2693           
=======================================
  Hits         6849     6849           
  Misses       1578     1578           

Components	Coverage Δ
App: Storefront	79.28% <ø> (ø)
App: Admin	90.05% <ø> (ø)
App: Landing	∅ <ø> (∅)
Pkg: @nordcom/commerce-db	93.91% <ø> (ø)
Pkg: @nordcom/commerce-errors	100.00% <ø> (ø)
Pkg: @nordcom/commerce-marketing-common	∅ <ø> (∅)
Pkg: @nordcom/commerce-shopify-graphql	100.00% <ø> (ø)
Pkg: @nordcom/commerce-shopify-html	94.93% <ø> (ø)
Layer: Apps	80.84% <ø> (ø)
Layer: Packages	81.74% <ø> (ø)

Flag	Coverage Δ
unit	81.27% <ø> (ø)

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

Files with missing lines	Coverage Δ
packages/cart/next/src/cookie-storage.ts	100.00% <ø> (ø)
packages/cart/next/src/form-actions.ts	46.73% <ø> (ø)
packages/cart/next/src/typed-actions.ts	65.85% <ø> (ø)