Add top & bottom toolbar components (OUDSToolBarTop / OUDSToolBarBottom) and docs

[pylapp]

Motivation

• Provide first implementation of top and bottom toolbars so navigation bars/toolbars are available as OUDS SwiftUI components.
• Offer a strongly typed item API so consumers can pass leading/trailing content with OUDS styling and predefined navigation items.

Description

• Add OUDSToolBarTop and OUDSToolBarBottom SwiftUI components plus OUDSToolBarItem and OUDSToolBarNavigationItem helpers for leading/trailing items and common icons (back, close, menu).
• Implement appearance modifiers ToolBarTopAppearanceModifier and ToolBarBottomAppearanceModifier that apply blur and bar.colorBgTranslucent for iOS < 26 while deferring to system (Liquid Glass) behavior on iOS 26+.
• Add ToolBarItemStyleModifier to apply colors.contentDefault and to apply colors.actionAccent as trailing background on iOS 26+, and introduce ToolBarTitleView to render title + optional subtitle using OUDS typography tokens.
• Update documentation in OUDS/Core/Components/Sources/_OUDSComponents.docc/Navigations.md with usage samples and notes about Liquid Glass and platform availability (iOS 15, macOS 15, visionOS 1, unavailable on watchOS/tvOS).

Testing

• Attempted to run formatting via bundle exec fastlane format but it failed because fastlane is not available due to bundle install failing with a 403 Forbidden from rubygems.org.
• Attempted bundle install but it failed with a 403 Forbidden error while fetching gems, so automatic format/build/test/lint pipelines were not executed.
• No unit or snapshot tests were run in this environment due to the dependency installation failure.
• The changes were locally compiled/committed in the working branch (file creation and integration points added) but CI validation still needs to be executed after dependencies are available.

---

Codex Task