refactor(extension): auto-index on tool call and skip registration when binary missing

- Only register tool if `codexis` binary is in PATH
- Run incremental index via `pi.exec` on each tool call to keep DB fresh
- Remove `findDatabase` helper; derive DB path from git root directly
- Replace `defineTool` with inline `pi.registerTool` call
- Update imports (`@sinclair/typebox`, lazy `execSync`)
- Fix output flag help text in main.go

main.go

@@ -20,7 +20,7 @@ const dbFileName = "index.db"
 
 func main() {
 	force := flag.Bool("force", false, "Force full re-index (ignore file hashes)")
-	output := flag.String("o", "", "Output database path (default: <root>/.codexis.db)")
+	output := flag.String("o", "", "Output database path (default: <root>/.codexis/index.db)")
 	flag.Parse()
 
 	root := "."