CLI: Add --search flag to filter models

[cardmagic]

Summary

Add a --search flag to the classifier models command to filter models by name or description.

Motivation

When a registry has many models, users need a way to quickly find relevant ones without scrolling through the full list.

Proposed Syntax

# Search in default registry
classifier models --search spam
# => spam-filter      Email spam detection (bayes, 245KB)

# Search in custom registry
classifier models @user/repo --search sentiment
# => sentiment-v1     Basic sentiment (bayes, 500KB)
# => sentiment-v2     Advanced sentiment (lsi, 1.2MB)

Implementation Notes

• Filter on both model name and description
• Case-insensitive matching
• Works with both remote and --local modes

Related

• Part of Add CLI executable for training and classification #119 CLI specification
• Follow-up from Add CLI executable with model registry support #127