feat: add daily auto-trigger with --schedule and --watch modes

[4444J99]

Summary

Adds the #1 priority feature from the README TODO list: auto-triggered daily summaries.

Three new CLI flags:

• --schedule — generates a macOS LaunchAgent plist or crontab entry (copy-paste install)
• --watch — foreground daemon that wakes at the configured time and runs summarization
• --time HH:MM — configurable schedule time (default: 09:00)

Usage

# Generate scheduling config (LaunchAgent on macOS, crontab on Linux)
cargo run -- /path/to/repo "git log --oneline -20" --schedule

# Run as foreground daemon (wakes daily at 9am)
cargo run -- /path/to/repo "git log --oneline -20" --watch

# Custom time
cargo run -- /path/to/repo "git log --oneline -20" --watch --time 17:30

Implementation

• Extracted run_summarize() from main() so both one-shot and watch modes share identical behavior
• --schedule: detects OS, generates appropriate config with correct binary path
• --watch: uses tokio::time::sleep to compute seconds until next occurrence, runs, then sleeps past the minute boundary to avoid re-trigger
• --help / -h: full usage docs
• Backward compatible — positional args work identically to before

Dependencies

• Added dirs = "5.0" for home directory resolution in LaunchAgent path generation

cargo check passes clean.

TODO Items Addressed

• Auto-trigger summaries daily (feat: save summaries to date-organized folders #1 priority)