feat: add directed monthly fee settlement

[cofob]

Summary

• Add directed monthly fee invoices with fixed safety/common/base components and selectable budget targets.
• Settle directed fee invoices as direct payer-to-destination component transactions with draft and completed flows.
• Add UI pages, Telegram selection notifications, random fallback task, and regression coverage.

Problem

• Refinance needed to support the accepted monthly contribution system without routing money through F0 twice, because the extra hop distorted stats and made contribution targets unclear.
• The UI also needed a clear target-selection and settlement workflow so users can choose a budget target, create settlement transactions, and complete them without repeated no-op actions.

Changes

• Added fee policy/allocation models, config defaults, seed targets, selection endpoint, fallback task, and balance reminder selection links.
• Converted invoice payment linkage to support multiple invoice-linked component transactions while keeping backward-compatible transaction_id/transaction_ids behavior.
• Added direct fee settlement for base, safety cushion, common consumables, and directed target components, including split-target progress under the payer entity.
• Added UI selection, invoice detail/pay, bulk fee invoice, entity fee display, and settlement-completion behavior.
• Added compatibility handling for existing Postgres constraints and Docker dev service setup.

Testing

• uv run isort --check-only . - passed
• uv run black --check . - passed
• uv run mypy --ignore-missing-imports --follow-imports=skip api/app/schemas/fee.py api/app/routes/fee.py ui/app/controllers/invoice.py - passed
• docker compose -f docker-compose.yml -f docker-compose.dev.yml exec -T api pytest tests - passed, 125 tests

Risks

• Medium: fee settlement changes invoice and transaction accounting paths; compatibility shims preserve existing invoice transaction reads, but production data should be reviewed after deploy.

Rollback

• Revert this PR to restore the previous single-transaction invoice behavior and remove directed fee allocation flows. Existing historical transactions are not migrated by this change.

Links

• Issue: N/A
• Related: N/A

Checklist

• Scope is focused and backwards compatibility reviewed
• Tests added/updated where needed
• Local checks passed
• Docs/config updated if behavior changed