fix(sidebar): resolve localized item titles

[IzumiSy]

Motivation

SidebarItem.title accepted only raw strings even though SidebarGroup.title accepts localized strings. Consumers therefore could not pass defineI18nLabels values to sidebar items without resolving them inside the AppShell context.

Resolves tailor-inc/platform-planning#1887.

Summary

• Accept LocalizedString title overrides in SidebarItem.
• Resolve function-based overrides using the active AppShell locale while preserving existing string behavior, including empty strings.
• Add locale and compatibility coverage, regenerate documentation, and include a patch changeset.

[github-actions]

Code Metrics Report

	main (820ddb3)	#564 (81b7beb)	+/-
Coverage	87.5%	87.5%	+0.0%
Test Execution Time	2m19s	2m17s	-2s

Details

  |                     | main (820ddb3) | #564 (81b7beb) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          87.5% |          87.5% | +0.0% |
  |   Files             |            206 |            206 |     0 |
  |   Lines             |           6078 |           6081 |    +3 |
+ |   Covered           |           5319 |           5322 |    +3 |
+ | Test Execution Time |          2m19s |          2m17s |   -2s |

Code coverage of files in pull request scope (95.4% → 96.0%, patch 100.0%)

Files	Coverage	+/-	Patch Coverage	Status
packages/core/src/components/sidebar/sidebar-item.tsx	96.0%	+0.5%	100.0%	modified

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Reported by octocov