fix(startup): show --model flag override on startup screen (#898)

The startup screen was only reading model from env vars and settings,
ignoring the --model CLI flag since it's parsed by Commander.js after
the banner prints. Now eagerly parses --model from argv before rendering
so the displayed model matches what the session will actually use.

src/components/StartupScreen.test.ts

@@ -14,6 +14,7 @@ const ENV_KEYS = [
   'GEMINI_MODEL',
   'MISTRAL_MODEL',
   'ANTHROPIC_MODEL',
+  'CLAUDE_MODEL',
   'NVIDIA_NIM',
   'MINIMAX_API_KEY',
 ]
@@ -186,3 +187,71 @@ describe('detectProvider — explicit dedicated-provider env flags', () => {
     expect(detectProvider().name).toBe('MiniMax')
   })
 })
+
+// --- modelOverride from --model flag ---
+
+describe('detectProvider — modelOverride from --model flag', () => {
+  test('modelOverride overrides default Anthropic model', () => {
+    const result = detectProvider('claude-opus-4-6')
+    expect(result.name).toBe('Anthropic')
+    expect(result.model).toContain('opus')
+  })
+
+  test('modelOverride alias is resolved for Anthropic', () => {
+    const result = detectProvider('opus')
+    expect(result.name).toBe('Anthropic')
+    expect(result.model).toContain('opus')
+  })
+
+  test('modelOverride takes priority over ANTHROPIC_MODEL env var', () => {
+    process.env.ANTHROPIC_MODEL = 'claude-haiku-4-5-20251001'
+    const result = detectProvider('claude-opus-4-6')
+    expect(result.name).toBe('Anthropic')
+    expect(result.model).toContain('opus')
+  })
+
+  test('modelOverride takes priority over CLAUDE_MODEL env var', () => {
+    process.env.CLAUDE_MODEL = 'claude-haiku-4-5-20251001'
+    const result = detectProvider('claude-opus-4-6')
+    expect(result.name).toBe('Anthropic')
+    expect(result.model).toContain('opus')
+  })
+
+  test('modelOverride works for OpenAI provider', () => {
+    process.env.CLAUDE_CODE_USE_OPENAI = '1'
+    process.env.OPENAI_API_KEY = 'test-key'
+    process.env.OPENAI_MODEL = 'gpt-4o'
+    const result = detectProvider('gpt-4-turbo')
+    expect(result.model).toContain('gpt-4-turbo')
+  })
+
+  test('modelOverride works for Gemini provider', () => {
+    process.env.CLAUDE_CODE_USE_GEMINI = '1'
+    const result = detectProvider('gemini-2.5-pro')
+    expect(result.model).toBe('gemini-2.5-pro')
+  })
+
+  test('modelOverride works for Mistral provider', () => {
+    process.env.CLAUDE_CODE_USE_MISTRAL = '1'
+    const result = detectProvider('mistral-large-latest')
+    expect(result.model).toBe('mistral-large-latest')
+  })
+
+  test('modelOverride works for GitHub provider', () => {
+    process.env.CLAUDE_CODE_USE_GITHUB = '1'
+    const result = detectProvider('gpt-4o')
+    expect(result.model).toContain('gpt-4o')
+  })
+
+  test('undefined modelOverride preserves default behavior', () => {
+    const result = detectProvider(undefined)
+    expect(result.name).toBe('Anthropic')
+    expect(result.model).toContain('sonnet')
+  })
+
+  test('no argument preserves default behavior', () => {
+    const result = detectProvider()
+    expect(result.name).toBe('Anthropic')
+    expect(result.model).toContain('sonnet')
+  })
+})