* fix(web): render empty-state in sidebar when no projects configured
A fresh-install user with zero projects saw a blank sidebar and had no
way to open AddProjectModal from it. The early-return was originally
projects.length <= 1 (#381), softened to === 0 in #927, but no empty-
state UI was added at the same time.
Replace the null branch with a small ProjectSidebarEmpty sibling that
reuses the existing header (with the + button wired to AddProjectModal),
shows a one-line explainer, and renders only the ThemeToggle in the
footer (the show-killed/show-done/settings buttons are meaningless with
zero projects).
* fix(web): mark sidebar + button SVGs aria-hidden
The decorative SVG inside the labeled + buttons (empty-state and
populated sidebar) should not be announced — screen readers should rely
on the button's aria-label. Adds aria-hidden="true" to both for
consistency.
* fix(web): always mount sidebar so empty-state renders on fresh installs
Dashboard previously gated the sidebar on projects.length >= 1, leaving
ProjectSidebarEmpty unreachable. ProjectSidebar handles both cases now,
so drop the gate and add a dashboard-level test for the zero-project
path.
* fix(web): honor collapsed prop in empty sidebar branch
ProjectSidebarEmpty discarded the collapsed prop, so on a fresh install
the wrapper shrank to 44px while the inner sidebar stayed 224px and
overlapped the main content. Render a 44px-wide rail with just the +
button when collapsed, matching the populated sidebar's collapse path.
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