v0.3.1

Diagnostics now cover the whole workspace: every .taskpaper file in the project gets due-date diagnostics at startup (not just open files), and closing a file keeps its diagnostics from the on-disk state. The project diagnostics panel (cmd-shift-m) is now a true cross-file view.

Known Zed scoping: files opened from outside the project worktree don't appear in the project diagnostics panel (in-buffer squiggles still work there).