Refactor: move projectsWithSessions to Zustand store

[parsakhaz]

Problem

projectsWithSessions is local useState in DraggableProjectTreeView.tsx (~2500 lines). Every session status change creates a new array reference, which has caused infinite re-render loops in multiple useEffect hooks that depend on it. We've patched this twice now with refs:

• 22ba70c - Diff panel infinite re-render (same pattern)
• 453869d - DraggableProjectTreeView infinite re-render (3 effects)

The ref pattern works but is a symptom fix — the underlying issue is structural.

Root Cause

Event handlers and effects need access to the latest projectsWithSessions data, but including it in dependency arrays causes cascading re-renders because every update produces a new array reference. We currently work around this by syncing a useRef on every render, which is fragile and easy to forget when adding new effects.

Proposed Solution

Move projectsWithSessions into a Zustand store. This gives us:

• Shallow selectors — components only re-render when the specific slice they subscribe to changes, not on every array reference change
• getState() — event handlers can read current state directly without closures or refs
• Single source of truth — no more local state + ref syncing pattern
• Eliminates the class of bug entirely — new effects/handlers can't accidentally depend on a stale or re-triggering reference

Scope

• Extract projectsWithSessions and archivedProjectsWithSessions state + all mutation logic from DraggableProjectTreeView.tsx into a new Zustand store (or extend sessionStore)
• Update all IPC event handlers that call setProjectsWithSessions to use store actions instead
• Remove the projectsWithSessionsRef / runningProjectIdRef workarounds
• Components subscribe to specific slices with shallow comparison

Notes

This would also be a step toward breaking up the 2500-line DraggableProjectTreeView component, since the data layer would be decoupled from the UI.