fix(log): preserve loguru context in stdlib intercept

[olivermeyer]

Why?
Stdlib log records emitted inside logger.contextualize() were silently losing all bound context fields — including base-config keys like project_name and version — because InterceptHandler.emit overwrote loguru's assembled extra dict with the stdlib record's own (usually empty) extra. This meant Stargate internal log lines could not be correlated to a pviz job_id even when emitted in the correct contextualize scope.

How?
Changed the patcher body from assignment (record_dict["extra"] = ...) to record_dict["extra"].update(...), preserving loguru's assembled context and layering stdlib's own extra on top (stdlib-wins on key collision). Updated the InterceptHandler docstring to document the contextvars propagation behaviour across asyncio.to_thread vs bare threads. Three regression tests cover the core fix, the base-context guard, and native/stdlib parity.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Files with missing lines	Coverage Δ
src/aignostics_foundry_core/log.py	93.18% <100.00%> (ø)

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud