docs(upstream): record the v0.52.2 release

[sunerpy]

Summary

This records the v0.52.2 release in docs/upstream-sync/UPSTREAM.md, as #294 did for v0.52.1. It adds a Current alignment bullet for #295 and a dated release entry: the release PR merge and tag SHA, workflow run 36942112539 (all twelve jobs on the first attempt), the published digest, and the black-box acceptance against the official v0.52.1. That acceptance covers each of #295's five fixes plus the 18 → 19 upgrade, following the table fixed in advance in the plan.

The diff only adds lines.

Verification

make tools-check fmt-check docs-check passes. UPSTREAM.md is in .oxfmtignore. /tmp/verify-0.52.2.sh passed against the downloaded release.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main     #297   +/-   ##
=======================================
  Coverage   95.31%   95.32%           
=======================================
  Files         161      161           
  Lines       99752    99752           
=======================================
+ Hits        95083    95087    +4     
+ Misses       4669     4665    -4     

see 2 files with indirect coverage changes

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