refactor(api): split monolithic handlers.go into focused modules

Break down the 627-line handlers.go into specialized modules:
- handlers_chat.go: chat and streaming endpoints
- handlers_config.go: configuration endpoints
- handlers_common.go: shared utilities
- handlers_info.go: info and status endpoints
- handlers_terminal.go: terminal/shell endpoints
- handlers_tools.go: tool-related endpoints

Also includes config improvements, orchestrator enhancements, and
web component updates.

💘 Generated with Crush

Assisted-by: MiniMax-M2.7 via Crush <crush@charm.land>

internal/platform/platform_test.go

@@ -1,6 +1,7 @@
 package platform
 
 import (
+	"strings"
 	"testing"
 )
 
@@ -43,16 +44,9 @@ func TestString(t *testing.T) {
 	if s == "" {
 		t.Error("String should not be empty")
 	}
-	if !contains(s, "linux") {
+	if !strings.Contains(s, "linux") {
 		t.Error("Should contain OS")
 	}
 }
 
-func contains(s, sub string) bool {
-	for i := 0; i+len(sub) <= len(s); i++ {
-		if s[i:i+len(sub)] == sub {
-			return true
-		}
-	}
-	return false
-}
+