Issue #3608060: Add a Troubleshooting page: stranded-join recovery and the wait-node vs WAITING distinction

Frank Mablyrequested to merge
issue/orchestra-3608060:3608060-troubleshooting-docs into 1.x

Follow-up to #3608046. Adds a Troubleshooting docs page (stranded-join recovery, and the completion self-heal) and a code comment clarifying the wait-node (PARKED) vs WAITING (join) distinction on isStalled(). Docs and one comment only; no behaviour change.

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