feat: switch AI provider from Anthropic to DeepSeek

- lib/claude/client.ts: replace Anthropic SDK with openai package pointed at DeepSeek baseURL
- 4 AI routes: port tool definitions, tool_choice, and output parsing to OpenAI function-calling format
- Drop thinking:{type:'adaptive'} (no DeepSeek equivalent); model string → deepseek-chat
- settings/route.ts: add DEEPSEEK_API_KEY to ALLOWED_KEYS
- migration: seed DEEPSEEK_API_KEY placeholder row in app_settings
- tests: update 3 AI route tests to mock createDeepSeekClient + OpenAI response shape

Voyage AI embedding path untouched (DeepSeek has no embeddings endpoint).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CPf5Rc8QPx6V8KLEEgfKEQ

tests/api/incidents/quality-check.test.ts

@@ -1,23 +1,39 @@
 import { describe, it, expect, vi } from 'vitest'
 
+const qualityOutput = { score: 8, passes: true, feedback: 'Clear description.', suggestions: [] }
+
 vi.mock('@/lib/supabase/server', () => ({
   createClient: vi.fn().mockResolvedValue({
     auth: {
       getUser: vi.fn().mockResolvedValue({ data: { user: { id: 'user-1' } }, error: null }),
     },
+    from: vi.fn().mockReturnValue({
+      select: vi.fn().mockReturnThis(),
+      eq: vi.fn().mockReturnThis(),
+      gte: vi.fn().mockResolvedValue({ count: 0 }),
+    }),
+    rpc: vi.fn().mockResolvedValue({ error: null }),
   }),
 }))
 
 vi.mock('@/lib/claude/client', () => ({
-  createAnthropicClient: vi.fn().mockReturnValue({
-    messages: {
-      create: vi.fn().mockResolvedValue({
-        content: [{
-          type: 'tool_use',
-          name: 'assess_quality',
-          input: { score: 8, passes: true, feedback: 'Clear description.', suggestions: [] },
-        }],
-      }),
+  createDeepSeekClient: vi.fn().mockReturnValue({
+    chat: {
+      completions: {
+        create: vi.fn().mockResolvedValue({
+          choices: [{
+            message: {
+              tool_calls: [{
+                type: 'function',
+                function: {
+                  name: 'assess_quality',
+                  arguments: JSON.stringify(qualityOutput),
+                },
+              }],
+            },
+          }],
+        }),
+      },
     },
   }),
 }))
@@ -38,7 +54,7 @@ describe('POST /api/incidents/ai/quality-check', () => {
     expect(res.status).toBe(422)
   })
 
-  it('returns quality assessment from Claude', async () => {
+  it('returns quality assessment from DeepSeek', async () => {
     const { POST } = await import('@/app/api/incidents/ai/quality-check/route')
     const req = new Request('http://localhost/api/incidents/ai/quality-check', {
       method: 'POST',