Add report testable-code command

[dacharyc]

Summary

Adds report testable-code command to analyze code examples on documentation pages from analytics data. This helps identify high-traffic pages with testable but untested code examples.

New Command

# Analyze pages from analytics CSV
./audit-cli report testable-code analytics.csv [monorepo-path]

# Output formats: text (default), json, csv
./audit-cli report testable-code analytics.csv --format json --output report.json

Features:

• Resolves URLs to source files via Snooty Data API (with 24-hour caching)
• Collects code examples (literalinclude, code-block, io-code-block)
• Determines product context from tabs, composables, and content directories
• Reports tested vs testable vs "maybe testable" examples

Refactoring

Extracted shared utilities to internal packages for reuse:

• internal/language - Language normalization and product mapping
• internal/snooty - Snooty.toml parsing
• internal/config/url_mapping.go - URL-to-source-file resolution
• internal/projectinfo/products.go - Content directory to product mapping
• internal/rst/yaml_steps_parser.go - YAML steps file parsing

Version

Bumps version to 0.3.0