feat: add Visual Basic language support (SCIP + LSP, zero-effort via scip-dotnet)

[jafreck]

Summary

Add Visual Basic support via the existing SCIP and LSP infrastructure — scip-dotnet and OmniSharp already handle VB.

Tooling

Component	Tool	Status
SCIP indexer	scip-dotnet (already in Lore's registry)	✅ Same indexer as C#
LSP server	OmniSharp csharp-ls (already in Lore's registry)	✅ Handles VB
Tree-sitter	tree-sitter-vb	Optional — SCIP path is sufficient

What to implement

• Add visualbasic / vb to SCIP language mappings in scip-source.ts inferLoreLanguage() and SCIP_LANG_MAP
• Add file extension .vb to EXT_TO_LANG in scip-source.ts and walker.ts
• Add visualbasic entry to LSP registry in src/indexer/lsp/registry.ts pointing to csharp-ls
• Add visualbasic to the SCIP indexer registry (same scip-dotnet entry as C#)
• Verify scip-dotnet emits VB documents with correct language string or empty (check Document.language field)

Effort

Minimal — configuration only. No new extractor code needed. scip-dotnet already indexes .vb files and OmniSharp already provides LSP for them.

Context

Complements existing C# support in the .NET ecosystem. Enterprise codebases often have mixed C#/VB solutions.