Build finance foundation schema and backend module structure

[theMattCode]

User story

As a developer, I want a complete finance foundation schema and backend module skeleton so the rest of the finance system can build on one coherent model.

Depends on

• None.

Scope

• Add a forward PostgreSQL migration under i12e/postgres/migrations.
• Replace the current service_finance.transactions MVP schema with the new foundation schema.
• Create tables for financial accounts, categories, ledger entries, ledger entry parts, balance snapshots, securities, positions, investment transactions, price snapshots, budgets, budget allocations, recurring plans, reminders, and imported candidates/source metadata placeholders.
• Keep currency explicit on monetary records and financial accounts.
• Add Rust finance module structure for accounts, ledger, budgets, reminders, investments, and dashboard reporting.
• Add domain types/enums and repository traits without building full feature behavior.
• Ensure sensitive finance details are not logged.

Non-scope

• Cockpit UI.
• CSV import, bank sync, or quote providers.
• Cached dashboard summary tables.
• Tax tracking.

Acceptance criteria

• Migrations create the replacement finance schema from an empty database.
• Current finance MVP table is removed or superseded by the new schema through a forward migration.
• Backend compiles with the new finance module structure.
• Domain types represent the resolved glossary in CONTEXT.md.
• Imported candidates cannot affect ledger, cashflow, or balance in the model.
• Used setup entities have archive fields/statuses rather than relying on hard deletion.