feat(panel): adaptive monitoring poll intervals (v1.x closure phase 1)

Replace fixed 5 s hx-trigger polling with data-poll markers and panel.js
scheduling: 5 s while active, 30 s when idle, none when tab is hidden.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/templates/status_body.html

@@ -1,5 +1,5 @@
 {{define "status_body"}}
-<div id="status-body" hx-get="/status/fragment" hx-trigger="every 5s" hx-swap="outerHTML">
+<div id="status-body" data-poll hx-get="/status/fragment" hx-trigger="load" hx-swap="outerHTML">
   <div class="card" id="overall">
     <h2>Overall <span class="st st-{{.OverallStatus}}">{{.OverallStatus}}</span></h2>
     <p class="muted">{{.OverallHeading}}</p>