fix(mir): preserve contextual Sink handoff ownership

[slepp]

Summary

• preserve exact ownership authority when contextual destructuring transfers a Sink through an owned Result carrier;
• correlate the matching move, neutralization, transferee, destination, and typed close receiver before suppressing carrier drop;
• fail closed for contradictory, shadowed, reused, unowned, non-Sink, and unrelated move shapes.

Verification

• focused contextual ownership/drop tests, contradiction negatives, and typed receiver checks
• native/LLVM close-count execution coverage
• same-head MIR suite (1,734 tests), Clippy, and formatting
• compatible examples codegen (84/84), repository tests (29/29), and clean-port blog integration (20/20)

Out of scope

• broad clone/copy-on-write policy, D242, ABI changes, unsafe/runtime changes, public examples pins, and unrelated ownership lowering.