fix: tighten Anthropic provider matching and fix look-at test isolation

- Replace overly broad .includes('anthropic') with exact provider ID
  matching against known Anthropic providers (anthropic, google-vertex-
  anthropic, aws-bedrock-anthropic) in context-limit-resolver
- Add afterEach cleanup for vision-capable-models cache in look-at
  tool tests to prevent cross-test state leakage

src/shared/context-limit-resolver.ts

@@ -8,7 +8,8 @@ export type ContextLimitModelCacheState = {
 }
 
 function isAnthropicProvider(providerID: string): boolean {
-  return providerID.toLowerCase().includes("anthropic")
+  const normalized = providerID.toLowerCase()
+  return normalized === "anthropic" || normalized === "google-vertex-anthropic" || normalized === "aws-bedrock-anthropic"
 }
 
 function getAnthropicActualLimit(modelCacheState?: ContextLimitModelCacheState): number {