Migrate to Supabase + add seed data and test users

[shibinsp]

Description

Complete Supabase integration for TaskPulse AI:

• Migrate from SQLite/JWT to Supabase (Auth, PostgreSQL, Storage)
• Fix pooler compatibility (statement_cache_size, SSL)
• Add seed script with admin role, test users, and sample data

Acceptance Criteria

• Database connects via Supabase Supavisor pooler
• SSL context handles self-signed pooler certs
• asyncpg statement_cache_size=0 for transaction-mode pooler
• 6 test users created (one per role)
• 14 sample tasks with comments, history, check-ins
• Seed script is idempotent (safe to re-run)