[jscarle]

Adds .NET 11 and EF Core 11 support, updates dependencies, and consolidates the older database suites into one SQL Server 2025 integration suite. Migrates snapshots to SourceGeneratorTestHelpers 11 without Verify and aligns Roslyn references to 4.14.0.

Prepares v9.0.0, updates CI and publishing, fixes symbol packaging, and includes all existing working-tree changes, including AGENTS.md and duplicate-package handling.

Validation:

• Restore and Release build: zero warnings and errors.
• All 88 tests passed (30 generator snapshots and 58 database integration tests).
• NuGet and symbol packages produced; a separate .NET 11 consumer built and ran using the packaged generator.
• Rider inspections reported no code warnings, but its Roslyn worker raised C# 15 compatibility errors, so that check is incomplete.

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