Add collapsible category submenus to navigation sidebar

[magmoe]

Summary

• Group the flat 52-item Core nav list into 7 collapsible categories (Maps & Scenes, Layers, Visualization, Widgets,
  Queries, Interaction, Location) with animated expand/collapse chevrons
• Pro NavMenu inherits the same grouping, with all 24 Pro pages slotted into the matching categories alongside Core pages
• Active page's group auto-expands on load; search auto-expands all groups with matching results
• Restyle active item indicator: gradient left border + subtle hover-style background instead of solid gray box
• Pinned Home link at top with divider separator
• Fix UniqueValueRenderers build error (missing ToUpperFirstChar extension)

Code quality

• Category lives on the PageLink record itself (not a separate dictionary), so new pages can't be added without a
  category assignment
• Category names use compile-time constants (Categories.Layers, etc.) to prevent typos
• Pro uses p with { Href = href } to preserve base page data, avoiding per-access dictionary allocation
• Shared RenderNavLink RenderFragment eliminates duplicated NavLink markup across templates

Files Changed

• NavMenu.razor.cs — PageLink record with Category field, Categories constants, expand/collapse state, grouping
  logic
• NavMenu.razor — Grouped rendering with collapsible headers, pinned items, shared RenderFragment
• site.css — Group header, sublist, pinned item, and active item styles
• ProNavMenu.razor.cs — Pro pages with category assignments, with expression for base page remapping
• ProNavMenu.razor — Matching grouped template with shared RenderFragment
• UniqueValueRenderers.razor.cs — Build fix

[Copilot]

Pull request overview

This PR refactors the sample navigation sidebar from a long flat list into collapsible category submenus (shared between Core and Pro samples), adds pinned top-level links, updates active-item styling, and includes a small build fix in a sample page.

Changes:

• Add Category to PageLink + grouping/expand-collapse state management in NavMenu.
• Update Core/Pro nav menu Razor templates to render grouped, collapsible sections with shared link rendering.
• Update sidebar CSS for group headers, nested lists, pinned items, and the new active indicator style.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
samples/pro/dymaptic.GeoBlazor.Pro.Sample.Shared/Shared/ProNavMenu.razor.cs	Assign categories to Pro pages and reuse base PageLink via with when rewriting Href.
samples/pro/dymaptic.GeoBlazor.Pro.Sample.Shared/Shared/ProNavMenu.razor	Render pinned items + grouped collapsible sections for Pro menu.
samples/core/dymaptic.GeoBlazor.Core.Sample.Shared/wwwroot/css/site.css	Add styles for group headers/submenus/pinned item and update active item indicator styling.
samples/core/dymaptic.GeoBlazor.Core.Sample.Shared/Shared/NavMenu.razor.cs	Introduce category constants, grouping order, expanded-group state, and auto-expand active group on load/search.
samples/core/dymaptic.GeoBlazor.Core.Sample.Shared/Shared/NavMenu.razor	Render pinned items + grouped collapsible sections for Core menu.
samples/core/dymaptic.GeoBlazor.Core.Sample.Shared/Pages/UniqueValueRenderers.razor.cs	Replace missing ToUpperFirstChar usage with an inline capitalization expression.

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