[CA-12] Integrate Supabase as internal database

[luigischmitt]

Goal

Add Supabase as the internal source of truth for complete charge and payment history, while keeping Google Sheets as public visualization.

Context

Currently we only use Google Sheets to track payments. This works, but:

• We don't have charge history (txid, creation date, etc.)
• Any manual edit to the spreadsheet can break the system
• We can't run complex queries (e.g., "how much did X pay in 2025?")

Proposed Architecture

Supabase (source of truth)      Google Sheets (visualization)
┌─────────────────────────┐     ┌─────────────────────────┐
│  members                │     │  Shared spreadsheet     │
│  charges                │ ──► │  (sync via jobs)        │
└─────────────────────────┘     └─────────────────────────┘

Database Schema

Table members

Field	Type	Description
id	uuid	PK
name	text	Member name
email	text	Member email
created_at	timestamp	Registration date

Table charges

Field	Type	Description
id	uuid	PK
member_id	uuid	FK → members
txid	text	Efí transaction ID
amount	decimal	Charged amount
month	text	Reference month (e.g., "FEB")
year	int	Reference year
status	text	pending, paid, expired
created_at	timestamp	Charge creation date
paid_at	timestamp	Payment date

Tasks

• Create Supabase project
• Create members and charges tables
• Add src/services/supabase.py with SupabaseService
• Add supabase to pyproject.toml
• Configure environment variables (SUPABASE_URL, SUPABASE_KEY)

Dependencies

None - can be done in parallel with other issues.