Add Floating IP scanning and a durable address registry with configurable history depth

Adds POST /api/v1/admin/ips/scan (plus an optional periodic ticker) to
discover free Floating IPs in the OpenStack project and feed them straight
into the check queue. More importantly, decouples check/event history from
ip_queue's lifecycle: a new ip_registry table (migration 0007) gives every
address ever submitted a durable identity, so deleting it from the queue no
longer destroys its history — it's still reachable via the new
GET /api/v1/admin/registry[/{ip}] endpoints and the dashboard's /registry
pages, with retention depth configurable in check cycles per address
(history_retention_cycles, 0 = unlimited).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/dashboard/templates/registry_detail.html

@@ -0,0 +1,56 @@
+{{define "registry_detail_page"}}
+<!doctype html>
+<html lang="ru">
+<head>{{template "html_head" .}}</head>
+<body>
+<div class="bg-grid"></div>
+<input type="checkbox" id="nav-toggle" class="nav-toggle">
+<div class="shell">
+{{template "sidebar_nav" .}}
+<div>
+{{template "topbar_mobile" .}}
+<main class="main">
+<div id="error-banner">{{template "banner_inner" .Banner}}</div>
+{{template "registry_detail_content" .}}
+</main>
+</div>
+</div>
+</body>
+</html>
+{{end}}
+
+{{define "registry_detail_content"}}
+<p><a href="/registry">&larr; К реестру</a></p>
+<div class="topbar">
+<h1 class="mono" style="display:flex;align-items:center;gap:10px">{{.History.Registry.IPAddress}}
+{{if .History.Registry.InQueue}}<a class="pill pill-info" href="/ips/{{.History.Registry.IPAddress}}">{{.History.Registry.CurrentState}} · в очереди</a>{{else}}<span class="pill pill-neutral">не в очереди</span>{{end}}
+</h1>
+</div>
+<p class="muted">
+впервые замечен: {{fmtTime .History.Registry.FirstSeenAt}} · последний раз замечен: {{fmtTime .History.Registry.LastSeenAt}}
+· всего циклов проверки: {{.History.Registry.TotalCycles}}
+</p>
+
+<h2 class="section-title">История проверок (все сохранённые циклы)</h2>
+{{if .History.Checks}}
+<div class="panel">
+<div class="table-scroll">
+<table>
+<thead><tr><th>Цикл</th><th>Источник</th><th>Тип</th><th>Цель</th><th>Успех</th><th>Задержка, мс</th><th>Время</th><th>Детали</th></tr></thead>
+<tbody>
+{{range .History.Checks}}
+<tr>
+<td class="num" data-label="Цикл">{{.CycleID}}</td>
+<td data-label="Источник">{{.Source}}</td><td data-label="Тип">{{.CheckType}}</td><td class="addr" data-label="Цель">{{.Target}}</td>
+<td data-label="Успех">{{if .Success}}<span class="pill pill-success">ok</span>{{else}}<span class="pill pill-danger">fail</span>{{end}}</td>
+<td class="num" data-label="Задержка, мс">{{.LatencyMS}}</td><td class="num" data-label="Время">{{fmtTime .CheckedAt}}</td><td data-label="Детали">{{.Detail}}</td>
+</tr>
+{{end}}
+</tbody>
+</table>
+</div>
+</div>
+<p class="muted" style="margin-top:8px">Если глубина истории (см. <a href="/settings">настройки</a>) ограничена, здесь
+показаны только сохранённые циклы — более старые уже вытеснены.</p>
+{{else}}<p class="muted">Проверок пока нет.</p>{{end}}
+{{end}}