Fix: new projects sort to top of sidebar

[Copilot]

New projects with no threads were sinking to the bottom of the sidebar because getProjectSortTimestamp() had no fallback for the threadless case — returning Number.NEGATIVE_INFINITY and losing to any project with thread activity.

What Changed

• Sidebar.logic.ts: getProjectSortTimestamp() uses project.updatedAt ?? project.createdAt as the sort key when a project has no threads, so a freshly created project carries its creation timestamp into the sort comparison rather than -Infinity
• Sidebar.logic.test.ts: Added the cross-scenario test that was missing — new project (no threads, createdAt = T+10min) vs. older project with a recent user message (T+5min); asserts new project sorts first
• TODO.md: Marked "New projects should go on top" complete

Why

updated_at sort derives its key from child thread user-message timestamps. A project with zero threads had no such timestamp, so it always fell below every project that had any thread activity at all. Using the project's own createdAt as a fallback makes the sort semantically consistent: a just-created project is treated as recently active until it accumulates thread history.

UI Changes

N/A

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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Project	Deployment	Actions	Updated (UTC)
okcode-marketing	Ready	Preview	Mar 31, 2026 9:58pm