fix: switch AI endpoints from tool-calling to JSON output mode

DeepSeek v4-pro reasoning model rejects tool_choice parameter.
All 4 endpoints now use system prompts with JSON schema
instructions and parse content as JSON instead of tool_calls.

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

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

@@ -61,67 +61,39 @@ export async function POST(
     res = await client.chat.completions.create({
       model: 'deepseek-v4-pro',
       max_tokens: 2048,
-      tools: [{
-        type: 'function',
-        function: {
-          name: 'draft_rca',
-          description: 'Draft a 5-Why root cause analysis and CAPA suggestions for an HSE incident',
-          parameters: {
-            type: 'object',
-            properties: {
-              five_why_steps: {
-                type: 'array',
-                items: {
-                  type: 'object',
-                  properties: {
-                    why: { type: 'string', description: 'The why question' },
-                    answer: { type: 'string', description: 'The finding or answer' },
-                  },
-                  required: ['why', 'answer'],
-                },
-                description: '3 to 5 why steps',
-              },
-              root_cause_summary: {
-                type: 'string',
-                description: 'One-sentence root cause statement',
-              },
-              capa_suggestions: {
-                type: 'array',
-                items: { type: 'string' },
-                description: 'Up to 3 corrective/preventive action suggestions',
-              },
-            },
-            required: ['five_why_steps', 'root_cause_summary', 'capa_suggestions'],
-          },
+      messages: [
+        {
+          role: 'system',
+          content: `You are an experienced HSE investigator for a Malaysian 3PL warehouse. Draft a 5-Why root cause analysis for incidents. You must respond with valid JSON only — no markdown, no explanation outside the JSON object.
+
+Output exactly this JSON structure:
+{
+  "five_why_steps": [
+    { "why": "<the why question>", "answer": "<the finding or answer>" }
+  ],
+  "root_cause_summary": "<one-sentence root cause statement>",
+  "capa_suggestions": ["<up to 3 corrective/preventive actions>"]
+}
+
+Provide 3–5 Why steps drilling from immediate cause to root cause. Frame CAPA suggestions appropriate for a Malaysian warehouse context.`,
         },
-      }],
-      tool_choice: { type: 'function', function: { name: 'draft_rca' } },
-      messages: [{
-        role: 'user',
-        content: `You are an experienced HSE investigator for a Malaysian 3PL warehouse. Draft a 5-Why root cause analysis for this incident.
-
-Site: ${incident.siteName ?? 'Unknown'}
-Zone: ${incident.zoneName ?? 'Unknown'}
-Incident type: ${incident.incidentType}
-Description: ${incident.description}
-Severity: ${incident.severity ?? 'not yet assigned'}/5
-Injury involved: ${incident.injuryInvolved ? `yes — ${incident.medicalStatus}` : 'no'}
-Fatality: ${incident.isFatality ? 'yes' : 'no'}
-Serious bodily injury: ${incident.isSeriousBodilyInjury ? 'yes' : 'no'}
-Triage notes: ${incident.triageNotes ?? 'none'}
-
-Provide 3–5 Why steps drilling from immediate cause to root cause. Give a one-sentence root cause statement. Suggest 3 corrective/preventive actions appropriate for a Malaysian warehouse context.`,
-      }],
+        {
+          role: 'user',
+          content: `Draft a 5-Why root cause analysis for this incident. Respond with JSON only.\n\nSite: ${incident.siteName ?? 'Unknown'}\nZone: ${incident.zoneName ?? 'Unknown'}\nIncident type: ${incident.incidentType}\nDescription: ${incident.description}\nSeverity: ${incident.severity ?? 'not yet assigned'}/5\nInjury involved: ${incident.injuryInvolved ? `yes — ${incident.medicalStatus}` : 'no'}\nFatality: ${incident.isFatality ? 'yes' : 'no'}\nSerious bodily injury: ${incident.isSeriousBodilyInjury ? 'yes' : 'no'}\nTriage notes: ${incident.triageNotes ?? 'none'}`,
+        },
+      ],
     })
   } catch {
     return NextResponse.json({ error: 'AI service unavailable' }, { status: 503 })
   }
 
-  const call = res.choices[0]?.message?.tool_calls?.[0]
-  if (!call || call.type !== 'function') return NextResponse.json({ error: 'AI draft failed' }, { status: 500 })
+  const raw = res.choices[0]?.message?.content
+  if (!raw) return NextResponse.json({ error: 'AI returned empty response' }, { status: 500 })
+
+  const json = raw.replace(/^```(?:json)?\s*/i, '').replace(/\s*```$/i, '').trim()
 
   let draft: { five_why_steps?: unknown; root_cause_summary?: unknown; capa_suggestions?: unknown }
-  try { draft = JSON.parse(call.function.arguments) }
+  try { draft = JSON.parse(json) }
   catch { return NextResponse.json({ error: 'AI returned unexpected structure' }, { status: 500 }) }
 
   if (