chore: remove dead code and consolidate duplicate types (#555)

- Delete unused files: lib/ai-config.ts, components/ui/card.tsx, lib/token-counter.ts
- Remove js-tiktoken dependency (only used by deleted token-counter.ts)
- Consolidate ProviderName type: add "ollama" to model-config.ts, import in ai-providers.ts
- Consolidate DiagramOperation type: keep in chat/types.ts, import in utils.ts and hook

lib/utils.ts

@@ -1,6 +1,9 @@
 import { type ClassValue, clsx } from "clsx"
 import * as pako from "pako"
 import { twMerge } from "tailwind-merge"
+import type { DiagramOperation } from "@/components/chat/types"
+
+export type { DiagramOperation }
 
 export function cn(...inputs: ClassValue[]) {
     return twMerge(clsx(inputs))
@@ -473,12 +476,6 @@ export function replaceNodes(currentXML: string, nodes: string): string {
 // ID-based Diagram Operations
 // ============================================================================
 
-export interface DiagramOperation {
-    operation: "update" | "add" | "delete"
-    cell_id: string
-    new_xml?: string
-}
-
 export interface OperationError {
     type: "update" | "add" | "delete"
     cellId: string