fix: rename deepseek model from deepseek-chat to deepseek-v4-pro

DeepSeek API deprecated deepseek-chat model. Returns error:
'the supported API model names are deepseek-v4-pro or deepseek-v4-flash'

Affected all 4 AI endpoints:
- risk-flags (90-day dashboard)
- triage-suggest
- rca-draft
- quality-check

Co-Authored-By: Claude <noreply@anthropic.com>

app/api/dashboard/ai/risk-flags/route.ts

@@ -109,7 +109,7 @@ export async function POST() {
   let res: Awaited<ReturnType<typeof client.chat.completions.create>>
   try {
     res = await client.chat.completions.create({
-      model: 'deepseek-chat',
+      model: 'deepseek-v4-pro',
       max_tokens: 2048,
       tools: [{
         type: 'function',
@@ -178,7 +178,7 @@ ${JSON.stringify(aggregates, null, 2)}
 
   await withUser(session.sub, async tx =>
     writeAuditLog(tx, 'incidents', session.sub, 'ai_risk_flags',
-      { flags, summary: input.summary, model: 'deepseek-chat' })
+      { flags, summary: input.summary, model: 'deepseek-v4-pro' })
   )
 
   return NextResponse.json({ flags, summary: input.summary })