feat(backend): add default store agents for seeding test databases (#11552)

This PR adds a collection of pre-built store agents that can be loaded
into test databases for development and testing purposes.

### Changes 🏗️

- Add 17 exported agent JSON files in `backend/agents/` directory
- Add `StoreAgent_rows.csv` containing store listing metadata (titles,
descriptions, categories, images)
- Add `load_store_agents.py` script to load agents into the test
database
- Add `load-store-agents` Makefile target for easy execution

**Included Agents:**
- Flux AI Image Generator
- YouTube Transcription Scraper  
- Decision Maker Lead Finder
- Smart Meeting Prep
- Automated Support Agent
- Unspirational Poster Maker
- AI Video Generator
- Automated SEO Blog Writer
- Lead Finder (Local Businesses)
- LinkedIn Post Generator
- YouTube to LinkedIn Post Converter
- Personal Newsletter
- Email Scout - Contact Finder Assistant
- YouTube Video to SEO Blog Writer
- AI Webpage Copy Improver
- Domain Name Finder
- AI Function

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
- [x] Run `make load-store-agents` and verify agents are loaded into the
database
  - [x] Verify store listings appear correctly with metadata from CSV
- [x] Confirm no sensitive information (API keys, secrets) is included
in the exported agents

#### For configuration changes:
- [x] `.env.default` is updated or already compatible with my changes
- [x] `docker-compose.yml` is updated or already compatible with my
changes
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

No configuration changes required - this only adds test data and a
loading script.

Author: Swiftyos

autogpt_platform/Makefile

@@ -1,4 +1,4 @@
-.PHONY: start-core stop-core logs-core format lint migrate run-backend run-frontend
+.PHONY: start-core stop-core logs-core format lint migrate run-backend run-frontend load-store-agents
 
 # Run just Supabase + Redis + RabbitMQ
 start-core:
@@ -42,7 +42,10 @@ run-frontend:
 
 test-data:
 	cd backend && poetry run python test/test_data_creator.py
-	
+
+load-store-agents:
+	cd backend && poetry run load-store-agents
+
 help:
 	@echo "Usage: make <target>"
 	@echo "Targets:"
@@ -54,4 +57,5 @@ help:
 	@echo "  migrate - Run backend database migrations"
 	@echo "  run-backend - Run the backend FastAPI server"
 	@echo "  run-frontend - Run the frontend Next.js development server"
-	@echo "  test-data - Run the test data creator"
+	@echo "  test-data - Run the test data creator"
+	@echo "  load-store-agents - Load store agents from agents/ folder into test database"