refactor(ai): replace manual reasoning switches with auto-inference

Remove the "Reasoning Model" and "Disable Thinking Mode" toggles from
the model config dialog. These switches were injecting `enable_thinking`
(a Qwen/DashScope-specific request parameter) into all providers,
causing 400 errors on OpenAI, Anthropic, Gemini, and other official
services.

Replace with automatic inference in buildPiModel:
- reasoning: true when the model's catalog capabilities include
  'reasoning'; falls back to a model-name heuristic for unlisted
  custom/self-hosted models (qwen3, qwq, deepseek-r, o1/o3, etc.).
- compat.thinkingFormat 'qwen': only set when reasoning is true AND
  the model is from the qwen provider or the model id contains
  "qwen"/"qwq". All other providers get compat: undefined and will
  never receive enable_thinking.

This means official reasoning models (o3, deepseek-reasoner, etc.) now
automatically get thinkingLevel:'medium', and self-hosted Qwen3
models continue to work as before — without any manual toggle.

Behavior change: models with 'reasoning' in their catalog capabilities
now default to thinkingLevel:'medium' (previously always 'off' unless
the manual switch was enabled).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/desktop/preload/apis/ai.ts

@@ -202,8 +202,6 @@ export interface AIServiceConfigDisplay {
   baseUrl?: string
   maxTokens?: number
   apiFormat?: string
-  disableThinking?: boolean
-  isReasoningModel?: boolean
   customModels?: Array<{ id: string; name: string }>
   createdAt: number
   updatedAt: number
@@ -721,8 +719,6 @@ export const llmApi = {
     baseUrl?: string
     maxTokens?: number
     apiFormat?: string
-    disableThinking?: boolean
-    isReasoningModel?: boolean
     customModels?: Array<{ id: string; name: string }>
   }): Promise<{ success: boolean; config?: AIServiceConfigDisplay; error?: string }> => {
     return ipcRenderer.invoke('llm:addConfig', config)
@@ -741,8 +737,6 @@ export const llmApi = {
       baseUrl?: string
       maxTokens?: number
       apiFormat?: string
-      disableThinking?: boolean
-      isReasoningModel?: boolean
       customModels?: Array<{ id: string; name: string }>
     }
   ): Promise<{ success: boolean; error?: string }> => {