Local analyze receipts are contractually tmp-only for issue-sourced epics

[sameera]

As an engineer running /nxs.analyze locally against an issue-sourced epic, I want
analyze-receipt.md to land under .nexus/tmp/ as a stated contract rather than incidental resolver
behavior, so that /nxs.close and /nxs.distill can depend on where it lives without
re-deriving it.

Acceptance Criteria

• Given a local (non---pr) /nxs.analyze run against an issue-sourced epic (materialized
  by the resolver, no committed entry), when the receipt is written, then it is written
  under .nexus/tmp/ beside the resolver-materialized epic.md, and the command's own
  documentation states this placement as intentional, not an artifact of where the epic happened
  to resolve.
• Given a local run against an old-contract entry whose epic.md is already committed under
  .nexus/queue/, when the receipt is written, then it is still written into that
  committed directory, unchanged from today.
• Given --pr mode, when analyze runs, then it continues to publish a PR review only
  (no receipt file) — unchanged from today.

Notes

Mostly a spec clarification pinning today's resolver behavior as a hard contract Story
STORY-170.02/STORY-170.03 depend on; expected to be low-risk / low-new-code. Part of epic #170.

[sameera]

Closed in 9733d70