Add Iowa Bridges sample + modernize PointsOnAMapBlog

[TimPurdum]

Summary

• New projects/IowaBridges sample — a .NET 10 Blazor Web App (InteractiveServer) using GeoBlazor Core 4.4.4 to visualize the FHWA National Bridge Inventory filtered to Iowa. Features a condition-based UniqueValueRenderer driven by an Arcade expression, a collapsible sidebar with condition/year/county filters (debounced), bridge popups with friendly labels, and a "Find Bridges at Risk" query that highlights matches via a GraphicsLayer ring and zooms to extent. Includes LayerList, Legend, Search, and ScaleBar widgets, plus a static IowaCounties FIPS map and a BridgeFilterState that always prefixes the Iowa state clause (STATE_CODE_001 = '19').
• Modernized projects/PointsOnAMapBlog — migrated from the legacy _Host.cshtml + Shared/ Server Blazor layout to the current Blazor Web App structure (Components/App.razor, Components/Layout/, Components/Pages/). No demo behavior changes; just project structure.
• Added top-level samples.slnx — solution file covering all Core and Pro sample projects so the samples/ tree can be opened as a single solution.
• Small fixes in Core samples — GeoJSONLayers.razor now uses the C# 12 collection-expression form for OrderBy; minor whitespace cleanup in dymaptic.GeoBlazor.Core.Sample.Shared.csproj.

Test plan

• cd projects/IowaBridges/IowaBridges && dotnet run -lp https — map loads centered on Iowa, only Iowa bridges render, condition colors visible.
• Toggle condition checkboxes, drag year slider, pick a county — filters apply via SetDefinitionExpression and the county selection zooms.
• Click a bridge — popup shows friendly labels and a formatted inspection date.
• Click Find Bridges at Risk — non-zero count appears, results are ringed in the accent color, map zooms to fit; Clear removes the ring.
• cd projects/PointsOnAMapBlog && dotnet run — all five demo pages (PointOnAMap, Line, Buffer, Antarctica, Comparison) still render and navigate.
• Open samples.slnx in Visual Studio / Rider — all Core and Pro sample projects load.

Note: projects/IowaBridges/IowaBridges/appsettings.Development.json and a couple of secrets.json files contain API/license keys — confirm those should ship in the repo, or move to user secrets before merging.

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