feat(spaces): move Space-Switcher into the PillNav start slot

Repositions the switcher from its floating spot in the top right of
the workbench into the bottom-fixed PillNav so it sits with the rest
of the nav chrome. Matches how every other persistent nav control
(app switcher, AI tier, sync status) lives in the PillNav.

Mechanics:
- @mana/shared-ui PillNavigation gains a `startSlot?: Snippet` prop
  rendered inside .pill-nav-container, before AppDrawer. Generic slot
  — any host component drops in.
- (app)/+layout.svelte passes the existing <SpaceSwitcher /> as the
  snippet (authenticated only). The old .space-bar wrapper above
  <main> is removed along with its CSS.
- SpaceSwitcher trigger is restyled to match Pill conventions: pill
  radius 999px, 32px height, 0.8125rem text, tighter paddings, shorter
  name cap (7rem). Visually merges with the surrounding Pills.
- Dropdown menu flips upward (bottom: calc(100% + 4px)) because the
  PillNav is position:fixed bottom — opening downward would land
  off-screen.

Type-check: 0 errors across 7200 files.
Scope tests: 10/10 pass.
Go tests + bun tests (mana-auth): all pass.

Plan: docs/plans/spaces-foundation.md

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

apps/mana/apps/web/src/lib/components/layout/SpaceSwitcher.svelte

@@ -174,15 +174,15 @@
 	.trigger {
 		display: inline-flex;
 		align-items: center;
-		gap: 0.5rem;
-		padding: 0.375rem 0.625rem;
-		border-radius: var(--radius-md, 6px);
-		background: var(--color-surface-2, transparent);
+		gap: 0.375rem;
+		padding: 0.25rem 0.5rem;
+		border-radius: 999px;
+		background: transparent;
 		border: 1px solid var(--color-border, hsl(0 0% 88%));
 		color: var(--color-text, inherit);
-		font-size: 0.875rem;
+		font-size: 0.8125rem;
 		cursor: pointer;
-		min-width: 8rem;
+		height: 32px;
 		transition: background-color 120ms ease;
 	}
 
@@ -195,7 +195,7 @@
 		overflow: hidden;
 		text-overflow: ellipsis;
 		white-space: nowrap;
-		max-width: 10rem;
+		max-width: 7rem;
 	}
 
 	.chev {
@@ -236,7 +236,9 @@
 
 	.dropdown {
 		position: absolute;
-		top: calc(100% + 4px);
+		/* Open upward because the switcher sits inside the bottom-fixed
+			 PillNav — a downward dropdown would land off-screen. */
+		bottom: calc(100% + 4px);
 		left: 0;
 		min-width: 14rem;
 		background: var(--color-surface-1, white);

apps/mana/apps/web/src/routes/(app)/+layout.svelte

@@ -981,7 +981,13 @@
 					{spotlightActions}
 					{contentSearcher}
 					positioning="static"
-				/>
+				>
+					{#snippet startSlot()}
+						{#if authStore.isAuthenticated}
+							<SpaceSwitcher locale={$locale === 'en' ? 'en' : 'de'} />
+						{/if}
+					{/snippet}
+				</PillNavigation>
 			</div>
 		{/if}
 
@@ -1000,11 +1006,6 @@
 			class="pt-2"
 		>
 			<div class="mx-auto max-w-7xl px-3 py-2 sm:px-6 sm:py-3 lg:px-8">
-				{#if authStore.isAuthenticated}
-					<div class="space-bar">
-						<SpaceSwitcher locale={$locale === 'en' ? 'en' : 'de'} />
-					</div>
-				{/if}
 				{#if routeBlocked && routeAppId}
 					<RouteTierGate
 						appName={routeAppId.name}
@@ -1054,12 +1055,6 @@
 <ToastContainer />
 
 <style>
-	.space-bar {
-		display: flex;
-		justify-content: flex-end;
-		margin-bottom: 0.5rem;
-	}
-
 	.bottom-stack {
 		position: fixed;
 		bottom: 0;