Core block: Navigation (dynamic, mobile aware)

[tayebmokni]

Summary

Implement the core/navigation block: edit-time UI to pick a menu (from #46) or build one inline, with desktop and mobile rendering modes. Dynamic block; render walks the assigned menu, resolves target to URLs, and emits accessible nav.

Design reference

• docs/04-block-editor.md §2.2 (Navigation)
• docs/03-theme-system.md §9.2 (Theme integration)

Acceptance criteria

• Block attributes: menuId, layout (horizontal | vertical), mobileBreakpoint, showSubmenuIcon
• Editor: menu picker; inline edit opens menu builder shortcut
• Dynamic render via the same menu walker that powers <NavMenu>
• Mobile hamburger toggle (interactive island)
• Submenu reveal: hover (desktop), tap (touch) — a11y compliant
• Renders selected menu's items resolved to permalinks
• Cache tag menu:{slug} (doc 07 conventions)

Dependencies

#134, #46

Complexity

L

[tayebmokni]

Closing — shipped in Wave P (#465/#466). PR body's auto-close only fired for the first issue.