Feature: watch mode — real-time event streaming to stdout

[davidgr4th]

Problem

Currently there's no way to stream new events in real-time.
You have to poll with a loop and --limit, which wastes requests
and adds 30s+ latency.

Proposal

Add a watch subcommand to adapters that support it:

web2cli discord watch --channel general
web2cli slack watch --channel random
web2cli hn watch --type top

Behavior:

• Prints new items to stdout as they appear (one JSON object per line)
• Runs until Ctrl+C
• Uses efficient polling internally (or WebSocket where possible)
• NDJSON format by default (newline-delimited JSON) for easy piping

Use cases

• AI agent reacting to Discord mentions in real-time
• Piping to other tools: web2cli slack watch | grep "deploy" | notify-send
• Monitoring dashboards in terminal
• Event-driven workflows without cron

Adapter YAML idea

commands:
  watch:
    description: Stream new messages
    mode: watch          # new mode type
    poll_interval: 5     # seconds between checks
    dedup_key: id        # field to deduplicate
    pipeline: [...]