feat: add hlz watch command for price alerts with shell triggers

[dzmbs]

Summary

Add hlz watch <COIN> --above|--below <PRICE> — a WebSocket-based price watcher that monitors a condition and optionally executes a shell command when triggered.

Changes

src/cli/args.zig

• Add WatchArgs struct with coin, above, below, cmd, repeat fields
• Add watch variant to Command union and HelpTopic enum
• Add parseWatch() with validation: exactly one of --above/--below required
• Wire into parse() and canonicalHelpTopic()

src/cli/commands.zig

• Add watch() command: connects to WS allMids, monitors target coin mid price
• Reconnect loop with max 10 retries, 2s backoff between attempts
• SIGINT handling reusing stream command pattern
• TTY output: ⚡ BTC hit 100234.50 (was watching: --above 100000)
• JSON output when piped or with --json: {"coin":"BTC","price":...,"condition":...,"threshold":...,"timestamp":...}
• Shell command execution via std.process.Child with /bin/sh -c
• --repeat flag for continuous monitoring
• 3 unit tests for extractMidPrice helper

src/cli/main.zig

• Wire .watch case in main command switch
• Rename STREAMING section to STREAMING & ALERTS
• Add watch command help documentation

Testing

• zig build test — all tests pass (186 including 3 new extractMidPrice tests)
• zig build hlz — builds successfully
• zig build hlz-terminal — builds successfully
• Arg validation: no args (exit 2), no condition (exit 2), both conditions (exit 2)
• hlz help watch — correct help output

Closes SYM-9

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Project	Deployment	Actions	Updated (UTC)
hlz	Ready	Preview, Comment	Mar 14, 2026 10:38pm

[dzmbs]

Closing for rework — fresh approach