feat(cli): blocks, numbered presets like ShellUI's dashboard-01

[Shewart]

Description

Blocks: numbered presets built from components, like ShellUI's dashboard-01.

Stacked on the edge-menu PR (base feat/edge-menu); this PR adds two commits.

• shellui-native add bottom-nav-01 writes one file to Components/Blocks/BottomNav01.cs (namespace <App>.Components.Blocks, next to Components/UI or Components/Native) and installs the components it uses. list shows blocks in a new Block category.
• Six blocks, code-built views on MAUI and Avalonia:
  • bottom-nav-01: app shell with a raised Pay button and an avatar tab.
  • bottom-nav-02: Material 3 tab bar.
  • bottom-nav-03: floating tab bar that hides on scroll; only the active tab is labelled.
  • bottom-nav-04: compact capsule; the active tab widens with its label.
  • bottom-nav-05: the active tab rises into a circle; the bar hides on scroll.
  • edge-menu-01: a page with a solid tool dock on its right edge.
• The bottom-nav blocks expose Pages (one view per tab Value), Nav and Show(value); 01 adds ActionClicked. edge-menu-01 exposes Page, Menu and ToolPicked.
• scripts/sync-templates.py reads Components/Blocks in both demos; block templates install to ../Blocks/<Name>.cs.
• Both demos have a Blocks section. The browser preview app (examples/Avalonia.Preview) compiles the blocks, so docs previews can use them.
• Docs: docs/COMPONENTS.md "Blocks", CLI README, roadmap.

Type of Change

• New feature (non-breaking change adding functionality)

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my code
• I have added comments where necessary
• I have updated the documentation (if applicable)
• My changes generate no new warnings
• I have tested on at least one platform (MAUI/WinUI/WPF)

Testing Done

• Solution builds with 0 warnings; 1559 main tests (new BlockTests: registry, install path, namespaces with Components/UI and Components/Native) and 174 headless tests (smoke renders of every block) pass; format clean.
• add bottom-nav-01 bottom-nav-03 bottom-nav-05 edge-menu-01 in a fresh Avalonia app and a fresh dotnet new maui app: four files in Components/Blocks, their components in Components/UI, both build 0/0 (MAUI on Windows and Android); list shows the blocks.
• Preview app builds with a block preview.
• Blocks checked in light and dark (Avalonia headless renders).