perf(tools): lower default result sizes to cut response tokens

The default limits let broad queries flood the model context. This
change sets smaller defaults. An explicit parameter still overrides each one.

- file_search: max_results 1000 to 50, context_lines 2 to 0.
- ast_query: max_results 100 to 50.
- ast_query compact output omits the node type unless verbose is set.

On a fixed seven-call suite, response size fell from 198529 to 61960 bytes.

internal/config/config.go

@@ -33,7 +33,7 @@ const (
 	DefaultSearchTimeout              = 30 * time.Second
 	DefaultMaxFileSize                = 10 * 1024 * 1024 // 10 MB
 	DefaultMaxParseSize               = 10 * 1024 * 1024 // 10 MB
-	DefaultMaxSearchResults           = 1000
+	DefaultMaxSearchResults           = 50
 	DefaultMaxEditSize                = 100 * 1024 // 100 KB
 	DefaultResourceLinkThresholdBytes = 64 * 1024  // 64 KiB
 )