style(ui): unify subpage tabs and tighten usage layout

Move agent detection into the client list, simplify usage filters and pagination, and route interface text through the shared type scale. Subpage navigation now uses underlined tabs instead of segmented controls.

tests/agent-configuration-layout-ui.cjs

@@ -32,7 +32,7 @@ const desktopViewports = [
       });
       await page.waitForFunction(() => window.fixtureCalls.some(call => call.cmd === 'get_agent_config_statuses')
         && document.querySelector('.agent-config-panel')?.getBoundingClientRect().height > 0
-        && !document.querySelector('.agent-header-actions button')?.disabled);
+        && !document.querySelector('.agent-client-list-heading button')?.disabled);
       await page.evaluate(() => document.fonts.ready);
     };
 

tests/agent-management-ui.cjs

@@ -16,7 +16,7 @@ const path = require('node:path');
     const open = async query => {
       await page.goto('http://localhost:1421/tests/fixtures/agent-backups.html?reset-selections&' + query);
       await page.waitForFunction(() => {
-        const refresh = document.querySelector('.agent-header-actions button');
+        const refresh = document.querySelector('.agent-client-list-heading button');
         return refresh && !refresh.disabled && document.querySelector('.agent-model-trigger, .agent-desktop-models')
           && window.fixtureCalls.some(call => call.cmd === 'get_agent_models');
       });

tests/agent-native-oauth-ui.cjs

@@ -28,7 +28,7 @@ const base = 'http://127.0.0.1:1421';
       await page.goto(`${base}/tests/fixtures/agent-backups.html?reset-selections&client=codex&${query}`, { waitUntil: 'domcontentloaded' });
       await update().waitFor();
       await page.waitForFunction(() => {
-        const button = document.querySelector('.agents-page .management-header button');
+        const button = document.querySelector('.agent-client-list-heading button');
         return window.fixtureCalls.some(call => call.cmd === 'get_agent_models') && button && !button.disabled;
       });
     };

tests/agent-navigation-ui.cjs

@@ -18,7 +18,7 @@ const assert = require('node:assert/strict');
       assert.equal(await page.locator('[role=tab][aria-selected=true]').count(), 1);
     };
     const ready = () => page.waitForFunction(() => {
-      const refresh = document.querySelector('.agent-header-actions button');
+      const refresh = document.querySelector('.agent-client-list-heading button');
       return refresh && !refresh.disabled && window.fixtureCalls.some(call => call.cmd === 'get_agent_models');
     });
     const open = async query => {