refactor(config)!: Enforce .taskmasterconfig and remove env var overrides

BREAKING CHANGE: Taskmaster now requires a `.taskmasterconfig` file for model/parameter settings. Environment variables (except API keys) are no longer used for overrides.

- Throws an error if `.taskmasterconfig` is missing, guiding user to run `task-master models --setup`." -m "- Removed env var checks from config getters in `config-manager.js`." -m "- Updated `env.example` to remove obsolete variables." -m "- Refined missing config file error message in `commands.js`.

assets/env.example

@@ -7,15 +7,4 @@ GROK_API_KEY=your_grok_api_key_here                 # Optional, for XAI Grok mod
 MISTRAL_API_KEY=your_mistral_key_here               # Optional, for Mistral AI models.
 AZURE_OPENAI_API_KEY=your_azure_key_here            # Optional, for Azure OpenAI models.
 AZURE_OPENAI_ENDPOINT=your_azure_endpoint_here      # Optional, for Azure OpenAI.
-
-# Optional - defaults shown
-MODEL=claude-3-7-sonnet-20250219  # Recommended models: claude-3-7-sonnet-20250219, claude-3-opus-20240229 (Required)
-PERPLEXITY_MODEL=sonar-pro        # Make sure you have access to sonar-pro otherwise you can use sonar regular (Optional)
-MAX_TOKENS=64000                   # Maximum tokens for model responses (Required)
-TEMPERATURE=0.2                   # Temperature for model responses (0.0-1.0) - lower = less creativity and follow your prompt closely (Required)
-DEBUG=false                       # Enable debug logging (true/false)
-LOG_LEVEL=info                    # Log level (debug, info, warn, error)
-DEFAULT_SUBTASKS=5                # Default number of subtasks when expanding
-DEFAULT_PRIORITY=medium           # Default priority for generated tasks (high, medium, low)
-PROJECT_NAME={{projectName}}      # Project name for tasks.json metadata
-OLLAMA_BASE_URL=http://localhost:11434/api # Base URL for local Ollama instance (Optional)
+OLLAMA_BASE_URL=http://localhost:11434/api          # Base URL for local Ollama instance (Optional)