docs: clarify hint matching, reserved IO pointers, and shared spool delivery

Address all five DOCS-NITS-0672 items by replacement:
- explain reserved/unemitted digest pointers and future open-turn absence;
- show api-level manifest/adapter option placement in hint help;
- publish one canonical keyword matching rule and cross-link monics;
- state bounded, non-digest-backed COMMUNE and IO payloads honestly;
- document poll/listen first-taker consumption of one spool.

Regenerate the CLI reference from freshly prebuilt workspace binaries.
Validated xtask check, traceability, clippy -p spt, mdbook, real CLI help
placement, and three rendered cross-links. No core wake or retention feature.

Co-authored by: todlando