perf: cache-stampede coalescing + DB safeguards; ui/i18n fixes

Backend — tail latency & throughput:
- FileContentCache, image transcode, and search now use moka single-flight
  (try_get_with / get_or_load) so N concurrent misses for the same key
  collapse to one disk read / transcode / query instead of a thundering herd.
  Microbenchmark (128 concurrent on one hot key): 128 loads / p99 ~1023ms
  before vs 1 load / p99 ~32ms after.
- DB: configurable per-statement timeout on the primary pool
  (OXICLOUD_DB_STATEMENT_TIMEOUT_SECS, default 30; maintenance pool exempt) so
  a runaway query can't pin a connection and starve the pool.
- DB: background pool-saturation monitor
  (OXICLOUD_DB_POOL_MONITOR_INTERVAL_SECS) that WARNs as the primary pool nears
  exhaustion — the early signal before tail latency cliffs.
- mimalloc: set MIMALLOC_PURGE_DELAY=0 (Dockerfile + compose) so freed pages
  return to the OS and RSS tracks the live working set; benchmarked on
  musl/aarch64 at ~400MB reclaimed vs 0MB with the default.

Frontend — UI / i18n fixes:
- i18n: fix literal "{{count}}" and "{{percentage}}/{{used}}/{{total}}" in the
  selection toolbar and storage line — the call sites passed param names that
  didn't match the locale placeholders; unify on `count` and pass the storage
  template its params. Add es files.selected_count.
- sidebar: hide the drive picker when there's only one drive (the redundant
  "Personal" row); remove the coloured left accent on the active nav item.
- logo: stop clipping the cloud's left bulge — viewBox recentred on the cloud's
  true bbox with proportional SVG size so it keeps the same rendered scale.
- user menu: drop the default <a> underline on the link rows.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/AppShell.svelte

@@ -261,7 +261,7 @@
 <div class="sidebar" class:open={sidebarOpen}>
 	<a href="/files" class="logo-container">
 		<div class="logo">
-			<svg viewBox="120 120 280 280" aria-hidden="true">
+			<svg viewBox="95 67 320 320" aria-hidden="true">
 				<path
 					d="M345 310c32 0 58-26 58-58s-26-58-58-58c-6.2 0-12 0.9-17.5 2.7C318 166 289 143 255 143c-34.3 0-63.1 22.6-73 53.7C176.9 195.7 171 195 165 195c-32 0-58 26-58 58s26 58 58 58h180z"
 				/>
@@ -302,7 +302,7 @@
 						session.user.storage_quota_bytes
 					)}
 				{:else}
-					{formatBytes(session.user.storage_used_bytes)} {t('storage.used', 'used')}
+					{formatBytes(session.user.storage_used_bytes)}
 				{/if}
 			</div>
 		</div>
@@ -526,7 +526,19 @@
 								<div class="user-menu-storage-fill" style:width="{storagePct}%"></div>
 							</div>
 							<div class="user-menu-storage-text">
-								{Math.round(storagePct)}% {t('storage.used', 'used')}
+								{#if session.user.storage_quota_bytes > 0}
+									{t(
+										'storage.used',
+										{
+											percentage: Math.round(storagePct),
+											used: formatBytes(session.user.storage_used_bytes),
+											total: formatBytes(session.user.storage_quota_bytes)
+										},
+										'{{percentage}}% used ({{used}} / {{total}})'
+									)}
+								{:else}
+									{formatBytes(session.user.storage_used_bytes)}
+								{/if}
 							</div>
 						</div>
 					{/if}
@@ -661,7 +673,7 @@
 	<div class="about-overlay" onclick={(e) => e.target === e.currentTarget && (aboutOpen = false)}>
 		<div class="about-modal" role="dialog" aria-modal="true" aria-labelledby="about-modal-title">
 			<div class="about-modal__logo">
-				<svg viewBox="120 120 280 280" aria-hidden="true">
+				<svg viewBox="95 67 320 320" aria-hidden="true">
 					<path
 						d="M345 310c32 0 58-26 58-58s-26-58-58-58c-6.2 0-12 0.9-17.5 2.7C318 166 289 143 255 143c-34.3 0-63.1 22.6-73 53.7C176.9 195.7 171 195 165 195c-32 0-58 26-58 58s26 58 58 58h180z"
 					/>
@@ -1071,8 +1083,10 @@
 	}
 
 	.about-modal__logo {
-		width: 64px;
-		height: 64px;
+		/* 73px (not 64) so the cloud keeps its rendered scale after the viewBox
+		   grew 280→320 to stop clipping its left bulge: 73/320 ≈ 64/280. */
+		width: 73px;
+		height: 73px;
 		color: var(--color-accent);
 	}