fix: correct model-preference IDs for all Perplexity models

Remove nemotron-4-ultra, add thinking variants for all models

Remove claude-sonnet-4.7 (only opus-4.7 with max), fix descriptions

Default to GPT-5.4, add kimi-k2.6/claude-sonnet-4.6/gemini-3.1-pro/nemotron-3-super/sonar2, remove grok/gemini-3.5, MCP model param support

v3: MCP server with auto-account, updated models