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

hooks/use-diagram-tool-handlers.ts

@@ -1,4 +1,5 @@
 import type { MutableRefObject } from "react"
+import type { DiagramOperation } from "@/components/chat/types"
 import { isMxCellXmlComplete, wrapWithMxFile } from "@/lib/utils"
 
 const DEBUG = process.env.NODE_ENV === "development"
@@ -29,12 +30,6 @@ type AddToolOutputParams = AddToolOutputSuccess | AddToolOutputError
 
 type AddToolOutputFn = (params: AddToolOutputParams) => void
 
-interface DiagramOperation {
-    operation: "update" | "add" | "delete"
-    cell_id: string
-    new_xml?: string
-}
-
 interface UseDiagramToolHandlersParams {
     partialXmlRef: MutableRefObject<string>
     editDiagramOriginalXmlRef: MutableRefObject<Map<string, string>>