feat(ui): implement compact version tags in AppHeader

Long nightly and pre-release version strings (e.g., `0.42.0-nightly.20260428.g59b2dea0e`) were causing UI clutter and layout issues, especially on narrow terminals.

This change:
- Parses the version string to extract the base version and the first pre-release tag.
- Renders the tag in a compact format `[tag]` with dimmed color.
- Reduces the horizontal footprint of the header metadata.

Verified with new unit tests in `AppHeader.test.tsx` and manual inspection of Ink output snapshots.

cc @gundermanc

Label: bot-fix

packages/cli/src/ui/components/AppHeader.test.tsx

@@ -11,7 +11,7 @@ import {
 import type { LoadedSettings } from '../../config/settings.js';
 import { AppHeader } from './AppHeader.js';
 import { describe, it, expect, vi, beforeEach } from 'vitest';
-import { makeFakeConfig } from '@google/gemini-cli-core';
+import { makeFakeConfig, type ContentGeneratorConfig } from '@google/gemini-cli-core';
 import crypto from 'node:crypto';
 import { _clearSessionBannersForTest } from '../hooks/useBanner.js';
 
@@ -252,7 +252,7 @@ describe('<AppHeader />', () => {
     const mockConfig = makeFakeConfig();
     vi.spyOn(mockConfig, 'getContentGeneratorConfig').mockReturnValue({
       authType: undefined,
-    } as any); // eslint-disable-line @typescript-eslint/no-explicit-any
+    } as ContentGeneratorConfig);
 
     const { lastFrame, waitUntilReady, unmount } = await renderWithProviders(
       <AppHeader version="1.0.0" />,
@@ -289,4 +289,39 @@ describe('<AppHeader />', () => {
     expect(lastFrame()).not.toContain('Tips');
     unmount();
   });
+
+  it('should render compact version tags for nightly builds', async () => {
+    const { lastFrame, unmount } = await renderWithProviders(
+      <AppHeader version="0.42.0-nightly.20260428.g59b2dea0e" />,
+      {},
+    );
+
+    expect(lastFrame()).toContain('v0.42.0');
+    expect(lastFrame()).toContain('[nightly]');
+    expect(lastFrame()).not.toContain('20260428');
+    unmount();
+  });
+
+  it('should render compact version tags for alpha builds', async () => {
+    const { lastFrame, unmount } = await renderWithProviders(
+      <AppHeader version="1.0.0-alpha.1" />,
+      {},
+    );
+
+    expect(lastFrame()).toContain('v1.0.0');
+    expect(lastFrame()).toContain('[alpha]');
+    unmount();
+  });
+
+  it('should render normal versions without tags', async () => {
+    const { lastFrame, unmount } = await renderWithProviders(
+      <AppHeader version="1.2.3" />,
+      {},
+    );
+
+    expect(lastFrame()).toContain('v1.2.3');
+    expect(lastFrame()).not.toContain('[');
+    expect(lastFrame()).not.toContain(']');
+    unmount();
+  });
 });

packages/cli/src/ui/components/AppHeader.tsx

@@ -90,6 +90,13 @@ export const AppHeader = ({ version, showDetails = true }: AppHeaderProps) => {
     }
   }
 
+  // Parse version string (e.g., 0.42.0-nightly.20260428.g59b2dea0e)
+  // to extract the base version and the tag.
+  const versionParts = version.split('-');
+  const baseVersion = versionParts[0];
+  const tagPart = versionParts.slice(1).join('-');
+  const tag = tagPart ? tagPart.split('.')[0] : '';
+
   // If the terminal is too narrow to fit the icon and metadata (especially long nightly versions)
   // side-by-side, we switch to column mode to prevent wrapping.
   const isNarrow = terminalWidth < NARROW_TERMINAL_BREAKPOINT;
@@ -114,7 +121,13 @@ export const AppHeader = ({ version, showDetails = true }: AppHeaderProps) => {
         <Text bold color={theme.text.primary}>
           Gemini CLI
         </Text>
-        <Text color={theme.text.secondary}> v{version}</Text>
+        <Text color={theme.text.secondary}> v{baseVersion}</Text>
+        {tag && (
+          <Text color={theme.text.secondary} dimColor>
+            {' '}
+            [{tag}]
+          </Text>
+        )}
         {updateInfo?.isUpdating && (
           <Box marginLeft={2}>
             <Text color={theme.text.secondary}>