92 event comparison over time

[dboghra]

Summary

Closes # 92

What changed:
Added an event time history visualization that lets coaches see an athlete's times for a single event across multiple completions. in trends section of the toggle on the athletes' profile. Includes a filter bar with an event type dropdown and an amount picker (last N runs or date range) or input a range, and a line chart showing run number vs total time in seconds with a reference line for the best time.

Why:
Coaches needed a way to track performance trends for a specific event over time, rather than viewing individual run analyses in isolation.

Technical decisions worth noting:
Any non-obvious choices and their rationale.
-Elapsed_ms is read directly from the run table since total run time is already stored there
-The chart only fetches data on explicit Apply click rather than reactively, to avoid unnecessary requests while the coach is still making selections

AI disclosure: Note what was AI-assisted vs. hand-written.
Feature architecture and file structure were AI-assisted via Claude. All code was reviewed, debugged, and integrated by hand, including resolving the useState placement bug, the elapsed_ms null handling, and the routing setup.

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