[Shewart]

Description

edge-menu: a tool dock on a screen edge for MAUI and Avalonia (EdgeMenu + EdgeMenuItem, shellui-native add edge-menu).

Stacked on the bottom-nav PR (base feat/bottom-nav); this PR adds one commit.

• A small handle on the screen edge slides out a rail of icon tiles.
• Side (Right / Left), Position along the edge, Variant Default (popover colors) or Solid (primary), Dim, CloseOnSelect, SelectedValue (optional), IsOpen.
• Placed over the page: only the handle and the open rail take input, so the page stays usable while it is closed.
• A tap outside, Escape (back on Android), the handle or a tile closes it.
• IsOpenChanged reports every open and close; SelectedValueChanged reports user input only; EdgeMenuItem.Clicked on every press.
• Avalonia: the handle and tiles are tab stops, Up / Down move between tiles, focus goes to the first tile on open and back to the handle on close.
• Also: demo sections on both platforms, the CLI template and registry entry, docs/COMPONENTS.md and the roadmap, headless tests.

Type of Change

• New component (adding a new UI component)

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; 1484 main tests and 168 headless tests pass; format clean.
• Headless tests: the handle opens it on both sides; a tile click raises Clicked and SelectedValueChanged once and closes it; values set from code raise nothing; a click outside and Escape close it; a button under the closed menu stays clickable.
• add edge-menu builds 0/0 in a fresh Avalonia app; add edge-menu bottom-nav in a fresh dotnet new maui app (Android and Windows).
• Checked in light and dark: Avalonia (headless renders) and the MAUI demo on Windows with both menus open.