feat(extraction): add Visual Basic .NET language support (.vb) (#648, #639, #170) (#1164)

Vendored patched govindbanura/tree-sitter-vbnet grammar (MIT, ~20-fix patch
+ new external scanner for XML literals and multi-line LINQ continuation;
provenance + rebuild instructions in docs/grammars/tree-sitter-vbnet.md),
vbnet extractor with VB-specific call/index disambiguation, Inherits/
Implements heritage, As New instantiation, events, Declare P/Invoke, and
MustOverride abstract members.

Parse health on five real repos: PolicyPlus 100%, CompactGUI 100%,
staxrip 95.2%, SCrawler 87.2%, PCL 87.5% (upstream grammar: 3-18%).
Retrieval A/B (sonnet): 26-43% faster with 0-5 file reads vs 7-20 without.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/extraction/languages/index.ts

@@ -30,6 +30,7 @@ import { objcExtractor } from './objc';
 import { cfscriptExtractor } from './cfscript';
 import { cfqueryExtractor } from './cfquery';
 import { cobolExtractor } from './cobol';
+import { vbnetExtractor } from './vbnet';
 
 export const EXTRACTORS: Partial<Record<Language, LanguageExtractor>> = {
   typescript: typescriptExtractor,
@@ -57,4 +58,5 @@ export const EXTRACTORS: Partial<Record<Language, LanguageExtractor>> = {
   cfscript: cfscriptExtractor,
   cfquery: cfqueryExtractor,
   cobol: cobolExtractor,
+  vbnet: vbnetExtractor,
 };