feat(api-access): unify DeepSeek model discovery and selection

- require explicit model discovery before saving DeepSeek connections
- preserve selected models when refreshing the catalog
- mark model lists stale when connection details change
- add model refresh support to easy mode
- apply built-in DeepSeek reasoning levels consistently

tests/modelService.test.ts

@@ -0,0 +1,60 @@
+import { describe, expect, it } from 'bun:test';
+import {
+  applyDeepSeekModelPreset,
+  DEEPSEEK_THINKING_LEVELS,
+  mergeModelOptions,
+  reconcileModelSelection,
+} from '../src/services/modelService';
+
+describe('model discovery selection', () => {
+  const discovered = [
+    { name: 'deepseek-chat' },
+    { name: 'deepseek-reasoner' },
+    { name: 'deepseek-new-model' },
+  ];
+
+  it('selects every discovered model on the first fetch for a new connection', () => {
+    expect(Array.from(reconcileModelSelection(discovered, [], [], 'initial'))).toEqual([
+      'deepseek-chat',
+      'deepseek-reasoner',
+      'deepseek-new-model',
+    ]);
+  });
+
+  it('keeps saved selections and leaves newly discovered models unchecked', () => {
+    expect(Array.from(reconcileModelSelection(
+      discovered,
+      [{ name: 'deepseek-chat' }],
+      ['deepseek-chat'],
+      'initial',
+    ))).toEqual(['deepseek-chat']);
+  });
+
+  it('preserves refresh selections, drops unavailable discoveries, and keeps configured models', () => {
+    expect(Array.from(reconcileModelSelection(
+      [{ name: 'deepseek-reasoner' }, { name: 'deepseek-new-model' }],
+      [{ name: 'custom-model' }],
+      ['DEEPSEEK-REASONER', 'removed-model', 'custom-model'],
+      'refresh',
+    ))).toEqual(['deepseek-reasoner', 'custom-model']);
+  });
+
+  it('deduplicates model names case-insensitively and keeps configured metadata', () => {
+    expect(mergeModelOptions(
+      [{ name: 'deepseek-chat' }],
+      [{ name: ' DEEPSEEK-CHAT ', alias: 'Chat' }],
+    )).toEqual([{ name: 'DEEPSEEK-CHAT', alias: 'Chat' }]);
+  });
+});
+
+describe('DeepSeek model preset', () => {
+  it('adds built-in thinking levels while preserving existing metadata', () => {
+    expect(applyDeepSeekModelPreset([{
+      name: 'deepseek-reasoner',
+      thinking: { custom: true, levels: ['legacy'] },
+    }])).toEqual([{
+      name: 'deepseek-reasoner',
+      thinking: { custom: true, levels: [...DEEPSEEK_THINKING_LEVELS] },
+    }]);
+  });
+});