docs: align architecture inventory with shipped Turn contracts (#2763)

* docs: align architecture inventory with shipped Turn contracts

Correct the seven-layer overview so pre-tick/next_probe is an optional
probe surface, and document LoopXTurnRoute/LoopXTurnResultKind instead of
treating the six-verb operator shorthand as the typed packet vocabulary.

Closes #2761

Co-authored-by: Cursor <cursoragent@cursor.com>

* docs: clarify next probe execution boundary

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Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: huangrt01 <huangrt01@163.com>