fix(client-web): prevent Plus One sidebar flicker during chat completion refresh

[DJJones66]

Summary

This PR fixes sidebar flicker in Plus One where each AI response completion caused a visible sidebar refresh/reload.

What changed

• Updated useProjects.refreshProjects() to keep existing project list visible during background refreshes (only show loading on initial empty load).
• Added a guard in selectProject() to no-op when re-selecting the currently active project.
• Added hook regression tests for:
  • no project-list loading flip during background refresh
  • no duplicate file fetch when selecting the active project

Files changed

• builds/typescript/client_web/src/hooks/useProjects.ts
• builds/typescript/client_web/src/hooks/useProjects.test.ts

Why this fixes it

Plus One calls refreshProjects() after conversation completion. Previously that toggled isLoadingProjects and swapped sidebar content to a loading state, causing visual flicker. Now refreshes are non-disruptive once data exists, and redundant project reselection no longer triggers file reload churn.

Validation

• npm test -- src/hooks/useProjects.test.ts
• npm test -- src/components/layout/Sidebar.test.tsx