feat: add cockpit triage backend foundation (Phase 1)

- Migration 071: add client_name, asset_name, issue_category,
  triage_hypothesis, evidence_items columns to ai_sessions
- TriageUpdate schema for AI-inferred header updates in chat responses
- QuestionItem.options field for quick-reply buttons
- PATCH /ai-sessions/{id}/triage endpoint for manual header edits
- POST /ai-sessions/{id}/handoff-draft streaming endpoint for conclude modal
- Structured handoff fields (root_cause, steps_taken, recommendations)
  on resolve/escalate requests, passed through to ResolutionOutputGenerator
- Triage fields exposed in AISessionDetail response for session resume

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/alembic/versions/071_add_triage_fields_to_ai_sessions.py

@@ -0,0 +1,31 @@
+"""add triage fields to ai_sessions for cockpit harness
+
+Revision ID: 071
+Revises: 070
+Create Date: 2026-04-01
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import JSONB
+
+
+revision = "071"
+down_revision = "070"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("ai_sessions", sa.Column("client_name", sa.String(255), nullable=True))
+    op.add_column("ai_sessions", sa.Column("asset_name", sa.String(255), nullable=True))
+    op.add_column("ai_sessions", sa.Column("issue_category", sa.String(100), nullable=True))
+    op.add_column("ai_sessions", sa.Column("triage_hypothesis", sa.Text(), nullable=True))
+    op.add_column("ai_sessions", sa.Column("evidence_items", JSONB(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("ai_sessions", "evidence_items")
+    op.drop_column("ai_sessions", "triage_hypothesis")
+    op.drop_column("ai_sessions", "issue_category")
+    op.drop_column("ai_sessions", "asset_name")
+    op.drop_column("ai_sessions", "client_name")