refactor: separate hooks and services across all features

[pysnooLab]

Summary

• Adds a `services/` folder per feature with plain async functions wrapping Supabase — no React dependencies
• Splits multi-action hook files into one file per action (e.g. `useCreateCustomer.ts`, `useUpdateCustomer.ts`)
• Hooks no longer import from `@/lib/supabase` directly — only from their feature's service layer
• Hook tests mock the service module; service tests mock `@/lib/supabase`
• Documents the convention in CLAUDE.md and updates the Testing section to reflect the new mocking strategy

Features refactored

• customers: `services/customers.ts` + 4 hooks (useCustomers, useCreateCustomer, useUpdateCustomer, useUserCompany)
• companies: `services/companies.ts` + `services/invites.ts` + 5 hooks (useCompanies, useCreateCompany, useUpdateCompany, useDeleteCompany, useCreateInvite)
• agents: `services/agents.ts` + 2 hooks (useAgents, useUpdateAgentCompanies)
• auth: `services/auth.ts` + `services/profile.ts` + `services/invite.ts` + updated useAuth, useProfile, AuthProvider, SignupForm

Test plan

• All 80 unit tests pass (`npm test`)
• Lint passes with 0 errors (`npm run lint`)
• TypeScript build succeeds (`npm run build`)
• Service tests mock `@/lib/supabase` directly
• Hook tests mock service modules (not supabase)
• E2E: login, customers CRUD, invite flow still work end-to-end

🤖 Generated with Claude Code