chore: upgrade AdvancedSearch.Server (Vue3) to .NET 8.0

[devin-ai-integration]

Summary

Upgrades the Vue3 AdvancedSearch.Server project from .NET 6.0 to .NET 8.0.

csproj changes:

• Target framework net6.0 → net8.0
• Microsoft.EntityFrameworkCore.Sqlite 6.0.1 → 8.0.11
• Microsoft.EntityFrameworkCore.SqlServer 6.0.1 → 8.0.11
• Microsoft.AspNetCore.SpaProxy 6.*-* → 8.0.11
• Removed Microsoft.AspNetCore.SpaServices.Extensions (dropped in .NET 8)

Startup.cs changes (to compensate for SpaServices.Extensions removal):

• Added app.UseDefaultFiles() before app.UseStaticFiles()
• Added endpoints.MapFallbackToFile("index.html") for SPA client-side routing

Third-party packages (Korzh.EasyQuery, EasyData, Korzh.DbUtils, Newtonsoft.Json) were left at their current versions as they target netstandard2.0 and compiled successfully against net8.0.

dotnet build passes with 0 errors (61 pre-existing nullable warnings).

Review & Testing Checklist for Human

• Run the app locally on .NET 8 and verify the Vue3 SPA loads correctly via SpaProxy — build passing does not confirm runtime behavior
• Verify MapFallbackToFile("index.html") doesn't intercept EasyQuery API routes (it shouldn't since fallback only matches when no other endpoint does, but worth confirming with a query request)
• Check the minor indentation inconsistency on the SpaProxy <PackageReference> line (8 spaces vs 4) — cosmetic only

Notes

• The commented-out UseSpa() / UseSpaStaticFiles() / UseVueCli() blocks in Startup.cs were already disabled before this change; they were left as-is since they're inert comments.
• System.Net.Http, System.Data.SqlClient, and System.Text.RegularExpressions are inbox on .NET 8 but were kept since the build succeeds and removing them is a separate cleanup concern.

Link to Devin session: https://app.devin.ai/sessions/f8059f78151e454898c9465ce6a1bd53
Requested by: @tobydrinkall

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.