Initial commit: MyMidas personal finance tracker

Full-stack self-hosted finance app with FastAPI backend and React frontend.

Features:
- Accounts, transactions, budgets, investments with GBP base currency
- CSV import with auto-detection for 10 UK bank formats
- ML predictions: spending forecast, net worth projection, Monte Carlo
- 7 selectable themes (Obsidian, Arctic, Midnight, Vault, Terminal, Synthwave, Ledger)
- Receipt/document attachments on transactions (JPEG, PNG, WebP, PDF)
- AES-256-GCM field encryption, RS256 JWT, TOTP 2FA, RLS, audit log
- Encrypted nightly backups + key rotation script
- Mobile-responsive layout with bottom nav

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/core/audit.py

@@ -0,0 +1,38 @@
+"""
+Append-only audit log writer.
+"""
+from __future__ import annotations
+import uuid
+from datetime import datetime, timezone
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from sqlalchemy.ext.asyncio import AsyncSession
+
+
+async def write_audit(
+    db: "AsyncSession",
+    *,
+    user_id: uuid.UUID | None,
+    action: str,
+    resource_type: str | None = None,
+    resource_id: uuid.UUID | None = None,
+    ip_address: str | None = None,
+    user_agent: str | None = None,
+    metadata: dict[str, Any] | None = None,
+    success: bool = True,
+) -> None:
+    from app.db.models.audit_log import AuditLog
+    log = AuditLog(
+        user_id=user_id,
+        action=action,
+        resource_type=resource_type,
+        resource_id=resource_id,
+        ip_address=ip_address,
+        user_agent=user_agent,
+        meta=metadata or {},
+        success=success,
+        created_at=datetime.now(timezone.utc),
+    )
+    db.add(log)
+    # Note: caller is responsible for committing