feat(minimax): Thinking-Parsing, 1h-Cache-TTL, Null-Safety, Provider-Integration

- Thinking-Streaming: Parse 'reasoning_details' (MiniMax mit reasoning_split),
  'reasoning' (Nvidia), 'reasoning_content' (DeepSeek/OpenAI-Compat),
  und inline <think>...</think>-Tags aus delta.content (Fallback)
- MiniMax: max_tokens=32768, stream_options={include_usage}, reasoning_split=true
- 1h-Prompt-Cache-TTL für API (extended-cache-ttl-2025-04-11 Header,
  Cache-Breakpoints auf System-Prompt + letztes Tool) und CLI (ENABLE_PROMPT_CACHING_1H=1)
- Null-Safety: choices/delta/tool_calls/usage null-Checks in Streaming + Non-Streaming
- finish_reason='length' → warning-Event + stopReason='max_tokens'
- MiniMax-Provider: BaseUrl, MinimaxApiKey-Setting, /api/models/minimax-Endpoint,
  Model-Dropdown, statische Fallback-Modelle, Cache-Laden mit Fallback
- Safety-Net: InvalidOperationException-Catch um SSE-Zeilen-Block

wwwroot/js/pages/agent-page.js

@@ -27,6 +27,7 @@ registerPage('agent', {
     const pollinationsOptgroup = document.getElementById('pollinationsOptgroup');
     const geminiOptgroup       = document.getElementById('geminiOptgroup');
     const openaiOptgroup       = document.getElementById('openaiOptgroup');
+    const minimaxOptgroup      = document.getElementById('minimaxOptgroup');
 
     // Modelle dynamisch laden
     const loadProviderModels = async (url, prefix, optgroup) => {
@@ -53,7 +54,8 @@ registerPage('agent', {
       loadProviderModels('/api/models/openai',       'openai',       openaiOptgroup),
       loadProviderModels('/api/models/nvidia',       'nvidia',       nvidiaOptgroup),
       loadProviderModels('/api/models/pollinations', 'pollinations', pollinationsOptgroup),
-      loadProviderModels('/api/models/gemini',       'gemini',       geminiOptgroup)
+      loadProviderModels('/api/models/gemini',       'gemini',       geminiOptgroup),
+      loadProviderModels('/api/models/minimax',      'minimax',      minimaxOptgroup)
     ]);
     const allowUserChoiceEl = document.getElementById('agentAllowUserChoice');
     const autoCommitEl = document.getElementById('agentAutoCommit');