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/incidents/[id]/ai/rca-draft/route.ts

@@ -59,7 +59,7 @@ 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',
@@ -135,7 +135,7 @@ Provide 3–5 Why steps drilling from immediate cause to root cause. Give a one-
   await withUser(session.sub, async tx => {
     await writeAuditLog(tx, 'incidents', id, 'ai_rca_draft', {
       root_cause_summary: draft.root_cause_summary as string,
-      model: 'deepseek-chat',
+      model: 'deepseek-v4-pro',
     })
   })