feat: Support custom claude project path

[potatogim]

Summary

Add --claude-dir CLI option to specify a custom Claude projects directory instead of the hardcoded ~/.claude/projects path.

Changes

• Add CLAUDE_PROJECTS_DIR environment variable support in ClaudeConversationExtractor
• Add --claude-dir CLI option to argparse
• Set environment variable when --claude-dir option is provided in main() and launch_interactive()
• Pass search_dir to search functions to respect custom directory setting

Motivation

Users may have Claude projects stored in non-default locations or want to analyze conversations from different Claude installations. This change allows specifying an alternative directory path.

Usage

# Using CLI option
claude-extract --claude-dir /path/to/.claude/projects --list

# Using environment variable
CLAUDE_PROJECTS_DIR=/path/to/.claude/projects claude-extract --list