[Gantt Chart] - 1.4.1 Investigate re-render code

Description

Before committing to a fix for the re-render cascade problem, we need to understand how state currently flows through the component tree; specifically, what's shared via context/props that causes editing one project to re-render others. This is a research ticket, not a fix. The goal is to come out with a clear picture of how hard the fix actually is to correctly scope the rest of 1.4. Time-boxed to the amount of one ticket - don't spend forever on this, just get a good sense of what's going on in the code.

Acceptance Criteria

• Document roughly where the shared state/context lives and what's bundled together in it
• Get a rough read on how big the fix looks

Proposed Solution

Install React DevTools Profiler, start recording, edit a project, and stop. This will show every component that re-rendered and why (context change vs prop change). Manually trace shared state and context in the code. Write up what you find in a doc or comment on this ticket.

Mocks

No response

Start by running the Gantt chart with React DevTools Profiler, record an edit to one project, and identify which components re-render and whether context or props are responsible. Trace the shared state and context through the component tree, then document where it lives, what it contains, and the approximate scope of a fix in a project document or this issue.