xAI Grok 4 Model Support

#950 699e9ee Thanks @ben-vargas! - Add support for xAI Grok 4 model
- Add grok-4 model to xAI provider with $3/$15 per 1M token pricing
- Enable main, fallback, and research roles for grok-4
- Max tokens set to 131,072 (matching other xAI models)
#946 5f009a5 Thanks @Crunchyman-ralph! - Add stricter validation and clearer feedback for task priority when adding new tasks
- if a task priority is invalid, it will default to medium
- made taks priority case-insensitive, essentially making HIGH and high the same value
#863 b530657 Thanks @OrenMe! - Add support for MCP Sampling as AI provider, requires no API key, uses the client LLM provider
#930 98d1c97 Thanks @OmarElKadri! - Added Groq provider support

#958 6c88a4a Thanks @Crunchyman-ralph! - Recover from @anthropic-ai/claude-code JSON truncation bug that caused Task Master to crash when handling large (>8 kB) structured responses. The CLI/SDK still truncates, but Task Master now detects the error, preserves buffered text, and returns a usable response instead of throwing.
#958 3334e40 Thanks @Crunchyman-ralph! - Updating dependency ai-sdk-provider-gemini-cli to 0.0.4 to address breaking change Google made to Gemini CLI and add better 'api-key' in addition to 'gemini-api-key' AI-SDK compatibility.
#853 95c299d Thanks @joedanz! - Unify and streamline profile system architecture for improved maintainability

Added support for xAI's Grok 4 model with competitive $3/$15 per 1M token pricing, available for main, fallback, and research roles.