docs(skill): add NavigationView usage recipe (#290)

* docs(skill): add NavigationView usage recipe

Agents struggle with NavigationView setup — trying incorrect
property init patterns. Add complete paste-ready recipe showing
SelectedTag, OnSelectionChanged, NavItem, and .Set() escape.

Fixes #280

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* refactor: move NavigationView recipe out of getting-started

Move inline NavigationView recipe to the reactor-navigation
skill where it belongs. The reactor-recipes skill already has
a full sidebar-nav.cs recipe.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: sundaramramaswamy

plugins/reactor/skills/reactor-navigation/SKILL.md

@@ -115,6 +115,11 @@ return NavigationView(
 `NavItem(label, icon?, tag?)` creates sidebar items. Icons are Segoe Fluent
 Icons names. The `NavigationView` handles selection state.
 
+**Manual wiring (without `UseNavigation`):**
+`SelectedTag` and `OnSelectionChanged` are record properties — use `with { }`.
+For the settings item: set `IsSettingsVisible = true` and check `args.IsSettingsSelected` (not via tag).
+Use `.Set(nv => nv.PaneDisplayMode = ...)` for non-record properties.
+
 ## 5. TabView (parallel tabs)
 
 Unlike stack navigation, tabs keep all content alive simultaneously: