fix(ai): extend timeout and token budget for thinking models

Thinking models like DeepSeek V4 Flash can exceed the 120s stream
timeout during long reasoning, causing truncated output and missing
answers. Increase stream timeout to 600s when thinking is enabled,
raise max_tokens floor to 8192, and bump reasoning display max-height.

Closes #326

apps/desktop/src/components/editor/AiAssistant.vue

@@ -738,7 +738,7 @@ const messageRenderer = createAiMessageRenderer({ markdown: formatInlineText });
                 <div
                   class="overflow-hidden transition-all duration-200 ease-in-out"
                   :style="{
-                    maxHeight: expandedReasoning.has(i) || msg.isThinking ? '2000px' : '0px',
+                    maxHeight: expandedReasoning.has(i) || msg.isThinking ? '20000px' : '0px',
                     opacity: expandedReasoning.has(i) || msg.isThinking ? '1' : '0',
                   }"
                 >