feat: add interactive model addition to model map

[laynepenney]

Summary

Add /modelmap add command to add models interactively without editing YAML files.

Usage

/modelmap add <name> <provider> <model> [description]
/modelmap add --global <name> <provider> <model> [description]

Examples

# Add to project config
/modelmap add coder ollama-cloud qwen3-coder:480b-cloud

# Add to global config with description
/modelmap add --global fast anthropic claude-3-5-haiku-latest "Quick tasks"

# Then use anywhere
/switch coder
/switch fast

Features

• Creates config file if it doesn't exist (minimal config with just models section)
• Validates provider name (anthropic, openai, ollama, ollama-cloud, runpod)
• Prevents duplicate model names
• Supports --global flag for ~/.codi/models.yaml
• Shows usage hint after adding

Test plan

• Build passes
• All 1781 tests pass
• /modelmap add validates provider
• /modelmap add --global creates ~/.codi/models.yaml if needed

🤖 Generated with Claude Code

[laynepenney]

Self-Review

• ✅ Build passes
• ✅ All 1781 tests pass
• ✅ Provider validation implemented
• ✅ Duplicate name detection works
• ✅ Creates minimal config if file doesn't exist
• ✅ --global flag works for both add and init
• ✅ Output shows usage hint (/switch <name>)
• No issues found. Ready to merge.