feat: alerts view + created-at timestamps on decisions

Mirror cscli alerts list: new /alerts endpoint hits LAPI machine auth
with since/ip/scenario/origin filters, renders ID, scope:value, reason,
country, AS, events, decisions, created_at.

Decisions table gains a Created column derived from until - duration
(LAPI does not expose created_at on /v1/decisions). Both views format
timestamps locally and append a relative "x ago" via Intl.RelativeTimeFormat,
refreshed every 30s on the decisions view.

app/templates/index.html

@@ -39,6 +39,37 @@
   </div>
   <div id="unban-me-result"></div>
 
+  <section>
+    <h2>Recent alerts</h2>
+    <form hx-get="/alerts" hx-target="#alerts" hx-trigger="submit, load delay:200ms" hx-swap="innerHTML" hx-indicator="#alerts" class="row">
+      <select name="since">
+        <option value="15m">15m</option>
+        <option value="1h" selected>1h</option>
+        <option value="6h">6h</option>
+        <option value="24h">24h</option>
+        <option value="168h">7d</option>
+        <option value="720h">30d</option>
+      </select>
+      <input type="text" name="ip" placeholder="IP (optional)">
+      <input type="text" name="scenario" placeholder="Scenario (optional)">
+      <select name="origin">
+        <option value="">any origin</option>
+        <option value="crowdsec">crowdsec</option>
+        <option value="cscli">cscli</option>
+        <option value="CAPI">CAPI</option>
+        <option value="lists">lists</option>
+      </select>
+      <select name="limit">
+        <option value="100">100</option>
+        <option value="200" selected>200</option>
+        <option value="500">500</option>
+        <option value="1000">1000</option>
+      </select>
+      <button type="submit">Search</button>
+    </form>
+    <div id="alerts">Loading…</div>
+  </section>
+
   <section>
     <h2>Active decisions</h2>
     <form hx-get="/decisions" hx-target="#decisions" hx-trigger="submit, load delay:200ms" hx-swap="innerHTML" hx-indicator="#decisions" class="row">