feat(hosting): implement POC builder service (Workstream 3C)

One-click POC site generation from prospect data + industry template:

PocBuilderService.build_poc():
1. Loads prospect (scraped content, contacts, business info)
2. Loads industry template (pages, theme, sections)
3. Creates HostedSite + Store via hosted_site_service
4. Populates CMS ContentPages from template, replacing {{placeholders}}
   (business_name, city, phone, email, address, meta_description,
   about_paragraph) with prospect data
5. Applies StoreTheme (colors, fonts, layout) from template
6. Auto-transitions to POC_READY status

API: POST /admin/hosting/sites/poc/build
Body: {prospect_id, template_id, merchant_id?}

Tested: prospect 1 (batirenovation-strasbourg.fr) + "construction"
template → 4 pages created, theme applied, subdomain assigned.

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

app/modules/hosting/routes/api/admin_sites.py

@@ -7,6 +7,7 @@ import logging
 from math import ceil
 
 from fastapi import APIRouter, Depends, Path, Query
+from pydantic import BaseModel
 from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_admin_api
@@ -24,6 +25,7 @@ from app.modules.hosting.schemas.hosted_site import (
 )
 from app.modules.hosting.schemas.template import TemplateListResponse, TemplateResponse
 from app.modules.hosting.services.hosted_site_service import hosted_site_service
+from app.modules.hosting.services.poc_builder_service import poc_builder_service
 from app.modules.hosting.services.template_service import template_service
 from app.modules.tenancy.schemas.auth import UserContext
 
@@ -42,6 +44,42 @@ def list_templates(
     )
 
 
+class BuildPocRequest(BaseModel):
+    """Request to build a POC site from prospect + template."""
+
+    prospect_id: int
+    template_id: str
+    merchant_id: int | None = None
+
+
+class BuildPocResponse(BaseModel):
+    """Response from POC builder."""
+
+    hosted_site_id: int
+    store_id: int
+    pages_created: int
+    theme_applied: bool
+    template_id: str
+    subdomain: str | None = None
+
+
+@router.post("/poc/build", response_model=BuildPocResponse)
+def build_poc(
+    data: BuildPocRequest,
+    db: Session = Depends(get_db),
+    current_admin: UserContext = Depends(get_current_admin_api),
+):
+    """Build a POC site from prospect data + industry template."""
+    result = poc_builder_service.build_poc(
+        db,
+        prospect_id=data.prospect_id,
+        template_id=data.template_id,
+        merchant_id=data.merchant_id,
+    )
+    db.commit()
+    return BuildPocResponse(**result)
+
+
 def _to_response(site) -> HostedSiteResponse:
     """Convert a hosted site model to response schema."""
     return HostedSiteResponse(