Canvas-based seasonal weather effects + demo page

Server picks variant from Lisbon-local date (rain/petals/jacaranda/motes/leaves)
and renders behind content via a canvas particle layer. Each variant has a
hand-drawn silhouette so shapes are recognizable. /weather demo route exposes
variant + intensity + phase pickers, locking the time-of-day phase override.

internal/web/templates/weather.html

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+{{define "title"}}Weather demo · {{.SiteTitle}}{{end}}
+
+{{define "main"}}
+<div class="space-y-8">
+  <section class="rounded-3xl bg-[color:var(--card)] p-6 shadow-pete border-2 border-[color:var(--ink)]/10">
+    <h1 class="font-display text-3xl font-bold mb-1">Weather demo</h1>
+    <p class="text-sm text-[color:var(--ink)]/60 mb-5">Pick a variant, intensity, and phase. The canvas reloads on each click.</p>
+
+    <div class="space-y-3 text-sm">
+      <div class="flex flex-wrap items-center gap-2">
+        <span class="w-20 shrink-0 font-semibold uppercase tracking-wider text-[color:var(--ink)]/60">Variant</span>
+        {{range $v := .Variants}}
+          <a href="?variant={{$v}}&amp;intensity={{$.Intensity}}&amp;phase={{$.PhaseSel}}"
+             class="rounded-full px-3 py-1 transition border-2 border-[color:var(--ink)]/10
+                    {{if eq $.Variant $v}}bg-[color:var(--accent)] text-white font-semibold{{else}}hover:bg-[color:var(--ink)]/5{{end}}">{{$v}}</a>
+        {{end}}
+      </div>
+      <div class="flex flex-wrap items-center gap-2">
+        <span class="w-20 shrink-0 font-semibold uppercase tracking-wider text-[color:var(--ink)]/60">Intensity</span>
+        {{range $i := .Intensities}}
+          <a href="?variant={{$.Variant}}&amp;intensity={{$i}}&amp;phase={{$.PhaseSel}}"
+             class="rounded-full px-3 py-1 transition border-2 border-[color:var(--ink)]/10
+                    {{if eq $.Intensity $i}}bg-[color:var(--accent)] text-white font-semibold{{else}}hover:bg-[color:var(--ink)]/5{{end}}">{{$i}}</a>
+        {{end}}
+      </div>
+      <div class="flex flex-wrap items-center gap-2">
+        <span class="w-20 shrink-0 font-semibold uppercase tracking-wider text-[color:var(--ink)]/60">Phase</span>
+        {{range $p := .Phases}}
+          <a href="?variant={{$.Variant}}&amp;intensity={{$.Intensity}}&amp;phase={{$p}}"
+             class="rounded-full px-3 py-1 transition border-2 border-[color:var(--ink)]/10
+                    {{if eq $.PhaseSel $p}}bg-[color:var(--accent)] text-white font-semibold{{else}}hover:bg-[color:var(--ink)]/5{{end}}">{{$p}}</a>
+        {{end}}
+      </div>
+    </div>
+
+    <div class="mt-5 text-xs text-[color:var(--ink)]/50">
+      Current: <code class="font-semibold">{{.Weather.Season}} / {{.Variant}} / {{.Intensity}} / {{.PhaseSel}}</code>
+    </div>
+  </section>
+
+  <section class="rounded-3xl bg-[color:var(--card)] p-10 shadow-pete border-2 border-[color:var(--ink)]/10 text-center">
+    <p class="font-display text-lg">Sample card</p>
+    <p class="mt-2 text-sm text-[color:var(--ink)]/60">Particles should drift in the margins around this block, not over the top of it.</p>
+  </section>
+
+  <section class="grid gap-4 sm:grid-cols-2">
+    <div class="rounded-3xl bg-[color:var(--card)] p-6 shadow-pete border-2 border-[color:var(--ink)]/10">
+      <p class="font-display">Card A</p>
+      <p class="text-sm text-[color:var(--ink)]/60 mt-1">Two cards with a gap so you can see the canvas between them.</p>
+    </div>
+    <div class="rounded-3xl bg-[color:var(--card)] p-6 shadow-pete border-2 border-[color:var(--ink)]/10">
+      <p class="font-display">Card B</p>
+      <p class="text-sm text-[color:var(--ink)]/60 mt-1">Move your window taller to give the particles more room.</p>
+    </div>
+  </section>
+</div>
+{{end}}