fix: protect sophia governor recent events

[sirakinb]

Fixes #6513.

Summary

• require the existing Sophia governor admin key before returning /sophia/governor/recent
• keep limit validation behind the auth check so unauthenticated callers cannot enumerate endpoint behavior
• add Flask regression tests for missing, wrong, and valid admin keys

Testing

• ./.venv/bin/python -m pytest -q tests/test_sophia_governor_recent_auth.py
• PYTHONPYCACHEPREFIX=/private/tmp/rustchain-pycache python3 -m py_compile node/sophia_governor.py tests/test_sophia_governor_recent_auth.py
• git diff --check

[eliasx45]

Reviewed the focused Sophia governor auth change at e0d3c4f510123c530ba5747307e3d868ff56dbea.

I did not find a blocker in the changed files. The new guard in node/sophia_governor.py runs before limit parsing, so unauthenticated callers get the same 401 for both normal and malformed limit requests, which matches the issue's goal of not exposing recent-event behavior. The new tests cover missing key, wrong key, valid admin key, and the auth-before-limit ordering.

Verification performed locally:

• .\.venv\Scripts\python.exe -m pytest tests/test_sophia_governor_recent_auth.py -q -> 3 passed
• .\.venv\Scripts\python.exe -m py_compile node/sophia_governor.py tests/test_sophia_governor_recent_auth.py -> passed
• git diff --check origin/main...HEAD -> clean
• Read Scottcjn/Rustchain#6513 and confirmed this PR gates /sophia/governor/recent with the existing RC_ADMIN_KEY / X-Admin-Key / X-API-Key helper used by the review/retry routes.

One merge note: GitHub's full pytest job is currently red during collection on node/gpu_render_endpoints.py:240 (SyntaxError: expected 'except' or 'finally' block). I confirmed the same syntax error exists when compiling that file from both origin/main and this PR head, so it is outside this two-file PR's diff. The focused regression for this PR is green locally.

[eliasx45]

Disclosure update for my review above: I am claiming RustChain ONBOARD review bounty #2782 for this review. RTC wallet: RTC9aa45a5fc499eeefff084f197ed15002e2a2309f.