[SAAS-018] feat: Add sales schema DDL
- Create sales schema (00-schema.sql)
- Add sales enums (01-enums.sql): lead_status, lead_source, opportunity_stage, activity_type, activity_status
- Add tables (02-tables.sql): pipeline_stages, leads, opportunities, activities
- Add functions (03-functions.sql): convert_lead_to_opportunity, update_opportunity_stage, calculate_lead_score, get_pipeline_summary, initialize_default_stages
- Add RLS policies (04-rls.sql) for tenant isolation
- Add indexes (05-indexes.sql) for performance
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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