fix: agent-inspector frontend assets missing from build (aws#883)

* fix: agent-inspector frontend assets missing from build

* fix: resolve React ref-during-render and setState-in-effect lint errors

- Wrap onReadyRef update in useEffect to avoid ref mutation during render
- Replace loggerRef.current access in return object with logFilePath state
- Replace useEffect+setState with state-based prev-step tracking pattern

Confidence: high
Scope-risk: narrow

---------

Co-authored-by: Jesse Turner <ajesstur@amazon.com>

Author: avi-alpert