feat(client): filter select_recipe by STATION_CODE with error fallback

Replace generic /api/recipes call with api_client.get_station_recipes(STATION_CODE).
Return 503 station_not_configured.html when STATION_CODE env var is unset.
Add station indicator to recipe selection page header.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/templates/errors/station_not_configured.html

@@ -0,0 +1,33 @@
+{% extends "base.html" %}
+{% block title %}{{ _('Stazione non configurata') }} — TieMeasureFlow{% endblock %}
+
+{% block content %}
+<div class="container mx-auto px-4 py-8 max-w-2xl">
+  <div class="mt-20 p-8 bg-[var(--bg-card)] rounded-xl shadow-lg text-center border border-red-200 dark:border-red-800">
+    <div class="inline-flex items-center justify-center w-16 h-16 rounded-full
+                bg-red-50 dark:bg-red-900/30 mb-6">
+      <svg class="w-8 h-8 text-measure-fail" fill="none" stroke="currentColor" stroke-width="1.75" viewBox="0 0 24 24">
+        <path stroke-linecap="round" stroke-linejoin="round"
+              d="M12 9v3.75m-9.303 3.376c-.866 1.5.217 3.374 1.948 3.374h14.71c1.73 0 2.813-1.874 1.948-3.374L13.949 3.378c-.866-1.5-3.032-1.5-3.898 0L2.697 16.126zM12 15.75h.007v.008H12v-.008z"/>
+      </svg>
+    </div>
+
+    <h1 class="text-2xl font-bold text-measure-fail mb-4">
+      {{ _('Stazione non configurata') }}
+    </h1>
+
+    <p class="mb-4 text-[var(--text-primary)]">
+      {{ _('Questo client non ha impostato la variabile di ambiente STATION_CODE.') }}
+    </p>
+
+    <p class="mb-6 text-sm text-[var(--text-secondary)]">
+      {{ _('Contattare il responsabile IT: il file .env del container deve contenere STATION_CODE con il codice della stazione assegnata.') }}
+    </p>
+
+    {% if error %}
+    <pre class="text-xs text-left text-[var(--text-secondary)] bg-[var(--bg-secondary)]
+                p-3 rounded-lg border border-[var(--border-color)] overflow-auto">{{ error }}</pre>
+    {% endif %}
+  </div>
+</div>
+{% endblock %}

client/templates/measure/select_recipe.html

@@ -75,6 +75,9 @@
           <p class="mt-1 text-sm text-[var(--text-secondary)]">
             {{ _('Scegli la ricetta di misura da eseguire') }}
           </p>
+          <p class="mt-1 text-sm text-steel-500 dark:text-steel-400">
+            {{ _('Stazione') }}: <span class="font-mono font-bold">{{ station_code }}</span>
+          </p>
         </div>
       </div>