feat: add procedural flow support to AI chat builder (Flow Assist)

- Add procedural-specific system prompts (schema, interview protocol, response format)
- Dispatch prompts by flow_type: procedural/maintenance use flat steps schema, troubleshooting uses decision tree schema
- Parse [STEPS_UPDATE] and [INTAKE_FORM] markers in AI responses
- Add validate_generated_procedural_steps() validator
- Handle intake form extraction in AI chat import endpoint
- Add StaticStepsPreview component for procedural flow preview
- Update store and page to render correct preview by flow type

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

backend/app/api/endpoints/ai_chat.py

@@ -390,11 +390,18 @@ async def import_tree(
     # Always create a new Tree record (no duplicate check — user may
     # want multiple copies or re-import after edits)
     metadata = session.tree_metadata or {}
+
+    # Extract intake form from metadata if present (procedural flows)
+    intake_form = None
+    if isinstance(metadata.get("intake_form"), list):
+        intake_form = metadata.pop("intake_form")
+
     tree = Tree(
         name=data.name or metadata.get("name", "AI-Generated Flow"),
         description=data.description or metadata.get("description", ""),
         tree_type=session.flow_type,
         tree_structure=session.working_tree,
+        intake_form=intake_form,
         author_id=current_user.id,
         account_id=current_user.account_id,
         category_id=data.category_id,