GC relocation: rewrite Promise and reaction graphs

Parent: #335 Depends on: #341 Roadmap: #144, #134

Complete Promise relocation without changing settlement or locking semantics.

Acceptance:

• Rewrite Promise value, wrapper, awaiting activation, forwarding Promise, and every inline/overflow reaction.
• Rewrite handler/extra argument/retained activation and the result-Promise or resolve/reject capability branch exactly as traced.
• Preserve detached-reaction semantics and Promise state/accounting metadata.
• Relocation runs only at the world-stopped commit boundary and does not acquire Promise locks.
• Distinct-target regressions prove inline and overflow branches.
• Focused normal and TSan runs report zero failures and leaks.
• Production movement remains disabled and #335 is updated.

Implemented and pushed in 8bacc09f.

Delivered:

• Promise value, wrapper, awaiting activation, forwarding Promise, inline reactions, and overflow reaction buffers all rewrite precisely;
• each reaction rewrites handler/extra/retained activation, then preserves the tracer-aligned result-Promise versus resolve/reject branch;
• relocation is explicitly world-stopped and takes no Promise state lock;
• distinct-target regression covers both storage forms and both capability branches.

Local gates:

• filtered normal: 3/3 passed, 0 failed, 0 leaked;
• filtered TSan: 3/3 passed, 0 failed, 0 leaked.

Production movement remains disabled. Keeping this open only for descendant full GitHub Actions evidence.

Completed and accepted. The implementation-specific local evidence is recorded above, and descendant full CI at https://github.com/zig-utils/zig-js/actions/runs/29716788619 completed with 42 successful jobs, one intentional nightly skip, zero failures, and zero cancellations.