docs: decide the lock-budgeted passthrough contract

[Kiran01bm]

Decide the contract for executing eligible refused schema changes through engine-owned bounded sessions.

Why

Operators currently have to copy a refused blocking statement into raw psql, losing pg-sprite's lock-queue protection and typed audit trail.

What

• Names the explicit acknowledgement --accept-blocking and keeps it distinct from --force.
• Limits v1 eligibility to typed lock-acquisition-bound refusals and excludes rewrite-class statements.
• Requires explicit non-zero lock_timeout and statement_timeout bounds in an engine-owned session.
• Defines executed-without-online-safety, retained refusal identity, and exit code 3.
• Records no-resume semantics and keeps the path out of SchemaBot v1.

Before / after

before: refused → operator runs raw psql with no budget
after:  refused → explicit flag → bounded session → marked verdict

Refs: docs/capabilities.md, docs/refusal-classes.md