Add batch upload and track --push features

[christse]

Features:

• Add batch upload via /_atomic endpoint for efficient multi-file uploads
• Add --push flag to track command for automatic server sync
• Cache JWT at startup in long-running processes (track, watch)
• Add -v/--verbose flag to sync, track, watch, push, pull commands

Batch upload features:

• Efficient batching with configurable batch size and payload limits
• Fallback strategy: full batch → half batches → individual uploads
• Verbose logging shows file lists, payload sizes, server responses
• Proper error handling with detailed error messages from /_atomic

Documentation:

• Update CLAUDE.md with track --push workflow
• Update README with verbose mode section and examples
• Document real-time local-to-server sync workflow