feat(banners): rotate active banners one at a time with a pager

Stacking every active banner vertically ate header height when several
were active at once. Only the highest-priority banner renders now; a
‹ 1/N › pager cycles through the rest, and all active banners are still
recorded in the notification-center history so cycled-away ones stay
reachable. Newly registered banners preempt the displayed one only when
they outrank it.

Also fix the startup flow: the restart-required banner (now priority 80)
outranks the model-folders setup warning (60), and the setup banner is
retired once a non-empty folder path is saved.

New banners.pager.* keys translated in all 9 locales.

tests/frontend/managers/BannerService.test.js

@@ -43,6 +43,7 @@ describe('BannerService', () => {
         // Reset banner service state
         bannerService.banners.clear();
         bannerService.initialized = false;
+        bannerService.currentBannerIndex = 0;
         bannerService.recentHistory = []; // Clear history for each test
         
         // Clear DOM
@@ -331,6 +332,116 @@ describe('BannerService', () => {
         });
     });
 
+    describe('Banner Rotation', () => {
+        const registerTestBanner = (id, priority) => {
+            bannerService.registerBanner(id, {
+                id,
+                title: `Banner ${id}`,
+                content: `Content ${id}`,
+                dismissible: true,
+                priority
+            });
+        };
+
+        const displayedBannerId = () =>
+            document.querySelector('#banner-container .banner-item')
+                ?.getAttribute('data-banner-id');
+
+        let dismissedStore;
+
+        beforeEach(() => {
+            dismissedStore = [];
+            storageHelpers.getStorageItem.mockImplementation((key, defaultValue) => {
+                if (key === 'dismissed_banners') {
+                    return dismissedStore;
+                }
+                return defaultValue;
+            });
+            storageHelpers.setStorageItem.mockImplementation((key, value) => {
+                if (key === 'dismissed_banners') {
+                    dismissedStore = value;
+                }
+            });
+            bannerService.container = document.getElementById('banner-container');
+            bannerService.initialized = true;
+        });
+
+        it('renders only the highest priority banner when multiple are active', () => {
+            registerTestBanner('low', 1);
+            registerTestBanner('high', 10);
+
+            const rendered = document.querySelectorAll('#banner-container .banner-item');
+            expect(rendered).toHaveLength(1);
+            expect(displayedBannerId()).toBe('high');
+        });
+
+        it('shows a pager with position indicator when multiple banners are active', () => {
+            registerTestBanner('a', 1);
+            registerTestBanner('b', 2);
+
+            const pager = document.querySelector('.banner-pager');
+            expect(pager).not.toBeNull();
+            expect(pager.querySelector('.banner-pager-indicator').textContent.trim())
+                .toBe('1 / 2');
+        });
+
+        it('does not show a pager for a single banner', () => {
+            registerTestBanner('only', 1);
+
+            expect(document.querySelector('.banner-pager')).toBeNull();
+        });
+
+        it('cycles to the next banner and wraps around', () => {
+            registerTestBanner('a', 1);
+            registerTestBanner('b', 2);
+
+            document.querySelector('[data-pager="next"]')
+                .dispatchEvent(new MouseEvent('click', { bubbles: true }));
+            expect(displayedBannerId()).toBe('a');
+            expect(document.querySelector('.banner-pager-indicator').textContent.trim())
+                .toBe('2 / 2');
+
+            document.querySelector('[data-pager="next"]')
+                .dispatchEvent(new MouseEvent('click', { bubbles: true }));
+            expect(displayedBannerId()).toBe('b');
+            expect(document.querySelector('.banner-pager-indicator').textContent.trim())
+                .toBe('1 / 2');
+        });
+
+        it('cycles backwards with the previous button', () => {
+            registerTestBanner('a', 1);
+            registerTestBanner('b', 2);
+
+            document.querySelector('[data-pager="prev"]')
+                .dispatchEvent(new MouseEvent('click', { bubbles: true }));
+            expect(displayedBannerId()).toBe('a');
+        });
+
+        it('shows the next banner after the displayed one is dismissed', async () => {
+            vi.useFakeTimers();
+            try {
+                registerTestBanner('a', 1);
+                registerTestBanner('b', 2);
+                expect(displayedBannerId()).toBe('b');
+
+                await bannerService.dismissBanner('b');
+                vi.advanceTimersByTime(300);
+
+                expect(displayedBannerId()).toBe('a');
+            } finally {
+                vi.useRealTimers();
+            }
+        });
+
+        it('records all active banners in history, not just the displayed one', () => {
+            registerTestBanner('a', 1);
+            registerTestBanner('b', 2);
+
+            const historyIds = bannerService.recentHistory.map(entry => entry.id);
+            expect(historyIds).toEqual(expect.arrayContaining(['a', 'b']));
+        });
+    });
+
     describe('Banner History', () => {
         const testBanner = {
             id: 'test-banner',