Items-list sparklines, retro CSS, pinned tooling, deploy docs

- Bulk-load recent price points per item and render a sparkline in
  the items list (new LoadRecentPriceHistory query avoids N+1).
- Add retro.css visual layer and refreshed login/items/layout styling.
- Swap the logo from webp to avif.
- Pin htmx/Chart.js/Tailwind/templ versions in the Makefile with
  vendor / tools / update-deps targets; README documents the
  dependency-bump flow and the hardened systemd deploy.

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

templates/layout.templ

@@ -23,6 +23,9 @@ templ head(title string) {
 		<link href="https://fonts.googleapis.com/css2?family=Outfit:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500;700&display=swap" rel="stylesheet"/>
 		<link rel="stylesheet" href="/static/css/tailwind.css"/>
 		<link rel="stylesheet" href="/static/css/app.css"/>
+		<!-- retro.css is an additive flair layer. Delete this <link> + the
+		     file to revert to the plainer look. See retro.css for details. -->
+		<link rel="stylesheet" href="/static/css/retro.css"/>
 		<script src="/static/vendor/htmx.min.js" defer></script>
 		<script src="/static/js/flair.js" defer></script>
 	</head>
@@ -30,10 +33,10 @@ templ head(title string) {
 
 templ Sidebar(active string) {
 	<nav class="v-side-nav flex flex-col">
-		<div class="px-4 py-5 flex items-center gap-2">
+		<a href="/" class="v-side-brand px-4 py-5 flex items-center gap-2">
 			<span class="text-2xl">🐝</span>
 			<span class="text-xl font-semibold tracking-wide">Veola</span>
-		</div>
+		</a>
 		<a href="/" class={ navClass("dashboard", active) }>Dashboard</a>
 		<a href="/items" class={ navClass("items", active) }>Items</a>
 		<a href="/results" class={ navClass("results", active) }>Results</a>