refactor(prospecting): migrate SVC-006 transaction control to endpoint level

Move db.commit() from services to API endpoints and Celery tasks.
Services now use db.flush() only; endpoints own the transaction.

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

app/modules/prospecting/services/enrichment_service.py

@@ -110,7 +110,7 @@ class EnrichmentService:
         if result["has_website"]:
             prospect.status = "active"
 
-        db.commit()
+        db.flush()
         return result
 
     def scan_tech_stack(self, db: Session, prospect: Prospect) -> ProspectTechProfile | None:
@@ -177,7 +177,7 @@ class EnrichmentService:
             profile.scan_source = "basic_http"
 
             prospect.last_tech_scan_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             return profile
 
         except Exception as e:
@@ -185,7 +185,7 @@ class EnrichmentService:
             if prospect.tech_profile:
                 prospect.tech_profile.scan_error = str(e)
             prospect.last_tech_scan_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             return None
 
     def scan_performance(self, db: Session, prospect: Prospect) -> ProspectPerformanceProfile | None:
@@ -251,13 +251,13 @@ class EnrichmentService:
             profile.scan_strategy = "mobile"
 
             prospect.last_perf_scan_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             return profile
 
         except Exception as e:
             logger.error("Performance scan failed for %s: %s", domain, e)
             prospect.last_perf_scan_at = datetime.now(UTC)
-            db.commit()
+            db.flush()
             return None
 
     def scrape_contacts(self, db: Session, prospect: Prospect) -> list[ProspectContact]:
@@ -339,7 +339,7 @@ class EnrichmentService:
                     break
 
         prospect.last_contact_scrape_at = datetime.now(UTC)
-        db.commit()
+        db.flush()
         return contacts
 
     def _detect_cms(self, html: str) -> str | None: