feat(sidebar): library + general settings dialogs, sidebar footer, alignment polish

- Add a Settings cog to the Folders header that opens a tabbed library
  admin dialog (Library / Index / Import / Logs) wrapping PhotoPrism's
  /api/v1 settings, index, import and errors endpoints.
- Add a sticky footer to the left sidebar with the signed-in user's
  display name plus quick-toggle theme, general-settings cog (separate
  dialog for app prefs), and sign-out. Pull these out of the top
  Toolbar trailing slot.
- Align depth-0 folder rows with the rest of the sidebar entries (drop
  the leading chevron column when no children) and bring heap rows in
  line with folder rows so the kebab is part of the row's hover
  background instead of a detached chip.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/routes/+layout.svelte

@@ -48,9 +48,10 @@
 						class="relative hidden h-full shrink-0 border-r border-border bg-card/30 md:block"
 						style="width: {view.leftSidebarWidth}px;"
 					>
-						<div class="h-full overflow-y-auto p-3">
-							<LeftSidebar />
-						</div>
+						<!-- LeftSidebar owns its own flex-col layout so its footer
+						     row (user/theme/settings/logout) can pin to the bottom
+						     while the nav above scrolls. -->
+						<LeftSidebar />
 						<div
 							class="group absolute -right-1.5 top-0 z-20 hidden h-full w-3 cursor-col-resize md:block"
 							use:resizable={{