Add test_seeds generator for automatic E2E seed data

[fez3d]

Summary

• Adds a new generator agent_e2e:test_seeds that reads all models and db/schema.rb, calls OpenAI to generate db/test_seeds.rb with realistic seed data for E2E testing
• The QA user (qa@example.com / Password123!) is always created directly by the generator, independent of the AI response — with automatic detection of Devise, has_secure_password, and confirmable
• Replaces the previous approach of relying on manually configured db/seeds.rb
• bin/e2e now requires db/test_seeds.rb to exist; if missing, it stops and shows the user exactly what to do based on whether OPENAI_API_KEY is configured or not
• The install generator delegates seed generation to the new test_seeds generator, keeping responsibilities separated

Changes

File	What changed
test_seeds/test_seeds_generator.rb	New generator — analyzes models, calls OpenAI (o3), generates db/test_seeds.rb
install/install_generator.rb	Delegates to agent_e2e:test_seeds, removes manual seed instructions from next steps
install/templates/e2e	Requires test_seeds.rb, exits with actionable instructions if missing
README.md	Documents the new generator, SEED_AI_MODEL config, and troubleshooting

Test plan

• Run bin/rails generate agent_e2e:install with OPENAI_API_KEY set — verify db/test_seeds.rb is generated with QA user and model data
• Run bin/rails generate agent_e2e:install without API key — verify it skips seed generation gracefully and shows instructions
• Run bin/rails generate agent_e2e:test_seeds independently — verify it generates/overwrites db/test_seeds.rb
• Run bin/e2e without db/test_seeds.rb — verify it exits with correct instructions
• Run bin/e2e with db/test_seeds.rb present — verify it seeds and runs tests normally
• Test with a Devise app — verify password_confirmation and confirmed_at are included in QA user block