[feature] watch: block until a run needs a human, with NDJSON state transitions #51

Split from #50 (item 1).

Problem

Meshloop has no command that waits for a run. In both live runs the origin agent wrote its own loop: run inspect --json every N seconds, diff node states with jq, and treat changes as events. Every orchestrator writes this loop again, and the result is only as good as status and inspect, which have known bugs (#46, #47).

Proposal

meshloop watch --graph <id> [--config <f>] [--db <f>] [--json] [--interval <s>]

• Prints the current state, then one NDJSON line per change to a node or plan state: {ts, graph_id, node, from, to, note}.
• Exits 0 when the run needs a person: any node is AwaitingReview, or the plan is awaiting_acceptance. Also exits 0 when the run finishes successfully.
• Exits non-zero when a node fails or runs out of retries, or when the graph can't be resolved.
• The last line gives the exit reason, e.g. {"exit": "awaiting_review", "nodes": [2]}.
• Reads the store only and never needs to own the worker process, so it works on run --detach runs.
• Update the meshloop-run and meshloop-status skills to use it instead of polling.

Relations

• Reads the same state as status. Its graph and config resolution should go through the fixed path from [bug] status ignores --config and reports ok with empty runs while a run is active #46, and its live value through the fix in [bug] inspect reports live: Dead for detached-run workers that are running #47.
• If the per-node waiting_for reason ([feature] status/inspect: report waiting_for per node and document R1 acceptance gating #52) has landed, include it in the exit line. Don't block on it.

Acceptance criteria

• Fixture test: a detached run where one node reaches AwaitingReview → watch exits 0 and its last line names that node.
• Fixture test: a node fails → non-zero exit, and the reason names the node.
• Unknown --graph → non-zero exit naming the graph id.
• Works when the config is outside the current directory, given --config.

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