feat(ai-session): add FlowPilot AI-powered troubleshooting sessions

Implements Phase 1 of the FlowPilot-First pivot — the core AI session
experience where engineers describe a problem and FlowPilot guides them
through structured diagnosis with selectable options, free-text escape
hatches, and auto-generated documentation on resolution.

Backend: AISession + AISessionStep models, FlowPilot Engine (LLM
orchestration with structured JSON output), Flow Matching Engine v1
(semantic + keyword + recency scoring), 8 API endpoints with auth,
rate limiting, and AI quota enforcement.

Frontend: Intake screen, conversational session view with sidebar,
step cards with options/actions/resolution suggestions, resolve/escalate
modals, documentation view with rating, session history integration,
and /pilot route with sidebar navigation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -36,6 +36,8 @@ from .survey_response import SurveyResponse
 from .survey_invite import SurveyInvite
 from .kb_import import KBImport, KBImportNode
 from .script_template import ScriptCategory, ScriptTemplate, ScriptGeneration
+from .ai_session import AISession
+from .ai_session_step import AISessionStep
 from .psa_connection import PsaConnection
 from .psa_post_log import PsaPostLog
 from .psa_member_mapping import PsaMemberMapping
@@ -90,6 +92,8 @@ __all__ = [
     "ScriptCategory",
     "ScriptTemplate",
     "ScriptGeneration",
+    "AISession",
+    "AISessionStep",
     "PsaConnection",
     "PsaPostLog",
     "PsaMemberMapping",