perf: Cache import mappings and index fuzzy matches for resolution

Two major optimizations for the ref resolution phase:

1. Cache extractImportMappings() results per file path — previously
   re-read and re-parsed the source file for every single ref from
   that file (e.g. 100 refs from one file = 100 identical file reads)

2. Replace linear scan in matchFuzzy() with a lazily-built
   case-insensitive Map index — O(1) lookup instead of iterating
   all function/method/class nodes for every unresolved ref.
   Also drop low-value prefix matching (confidence 0.3).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/resolution/index.ts

@@ -16,8 +16,8 @@ import {
   ResolutionContext,
   FrameworkResolver,
 } from './types';
-import { matchReference } from './name-matcher';
-import { resolveViaImport } from './import-resolver';
+import { matchReference, clearFuzzyIndex } from './name-matcher';
+import { resolveViaImport, clearImportMappingCache } from './import-resolver';
 import { detectFrameworks } from './frameworks';
 import { logDebug } from '../errors';
 
@@ -106,6 +106,8 @@ export class ReferenceResolver {
     this.qualifiedNameCache.clear();
     this.kindCache.clear();
     this.nodeByIdCache.clear();
+    clearImportMappingCache();
+    clearFuzzyIndex();
     this.cachesWarmed = false;
   }