web: unify page headers into one shared page-header bar

Every full-page view now renders the same sticky top bar (back button,
title, right-side actions) from the new web/css/page-header.css,
replacing a dozen per-page duplicates (.page-panel-header,
.project-page-header, .task-page-header, .llm-page-header, .um-header,
.apr-header, .llmr-header, .pv-header, .sa-header, .config-page-header,
.agents-page-header). Pages that padded the whole container (config,
agents, system-agents, llm-requests, models-hub) move that padding into
a body wrapper so the bar sits flush and stays pinned on scroll.
Back buttons are standardized to the icon-only .page-header-back.

web/components/approval-rules.js

@@ -1042,20 +1042,21 @@ export class ApprovalRulesPage extends LightElement {
 
     return html`
       <div class="apr-page">
-        <div class="apr-header">
-          <button
-            class="btn btn-sm btn-outline-secondary"
-            style="flex-shrink:0"
-            @click=${() => this._goBack()}
-          >
-            <i class="bi bi-arrow-left"></i>
-          </button>
-          <h2 class="apr-title">
-            ${isDefault ? html`<span class="apr-group-default-badge" style="vertical-align:middle">${t('approval.header.default_badge')}</span>` : nothing}
-            ${group.name}
-          </h2>
-          <div class="apr-header-right">
-            <span class="apr-header-count">${totalRules === 1 ? t('approval.header.rule_count', { n: totalRules }) : t('approval.header.rule_count_plural', { n: totalRules })}</span>
+        <div class="page-header">
+          <div class="page-header-left">
+            <button
+              class="btn btn-sm btn-outline-secondary page-header-back"
+              @click=${() => this._goBack()}
+            >
+              <i class="bi bi-arrow-left"></i>
+            </button>
+            <h2 class="page-header-title">
+              ${isDefault ? html`<span class="apr-group-default-badge" style="vertical-align:middle">${t('approval.header.default_badge')}</span>` : nothing}
+              ${group.name}
+            </h2>
+          </div>
+          <div class="page-header-actions">
+            <span class="page-header-count">${totalRules === 1 ? t('approval.header.rule_count', { n: totalRules }) : t('approval.header.rule_count_plural', { n: totalRules })}</span>
           </div>
         </div>