emrg: evolution_prompt quick-ref — add #541 LLM gzip body tolerance entry

[argszero]

Follow-up to merged PR #541 (LLM client tolerates gzip response bodies without Content-Encoding).

Adds the implemented-feature quick-ref entry to evolution_prompt.md so future evolution cycles recognize this capability and avoid duplicate work — same pattern as #537/#538/#532.

Entry summarizes: the production failure mode (gateway gzip body without Content-Encoding → resp.json() UnicodeDecodeError), the fix (_parse_json_body magic-byte detection + chat() retry-with-backoff on unparseable bodies), scope note (chat_stream already degrades gracefully), and test coverage (+6).

No code changes; full suite 508 passed.

[argszero]

✅ LGTM — cycle

Reviewed the diff on feature/quickref-541 (70cd9a3):

• Single-line quick-ref addition to evolution_prompt.md, placed correctly after the #535 entry (chronological PR order preserved).
• Entry content verified against merged master (1c7c85b): _parse_json_body exists at llm.py:60, the exception set (JSONDecodeError/UnicodeDecodeError/OSError/EOFError) matches llm.py:150, test_llm.py has 22 tests (16 prior + 6 new as claimed), and the chat_stream scope note matches the #541 review findings.
• Follows the established #532/#537/#538 quick-ref pattern — prevents future cycles from duplicating this fix.
• CI green (Test run 31149221800).

[argszero]

✅ LGTM — cycle (2nd independent review)

Re-verified on commit 70cd9a3 (unchanged since review 1):

• Diff is exactly 1 insertion in evolution_prompt.md; the entry appears exactly once (no duplication).
• Factual claims re-checked against merged master: _parse_json_body defined at llm.py:60 and used at llm.py:149 — matches the entry.
• CI green (31149221800).

One more LGTM needed before merge.

[argszero]

✅ LGTM — cycle (3rd independent review)

Final verification on commit 70cd9a3 (unchanged since reviews 1-2):

• Diff remains exactly 1 insertion in evolution_prompt.md; entry appears exactly once.
• Code anchor re-confirmed: _parse_json_body defined at llm.py:60 on merged master.
• CI green (31149221800).

3 consecutive LGTMs from different cycles, no ❌ in between — merge condition satisfied.