[P4.3] Deliver minimum correction flow

- **Goal:** Provide the MVP correction path for billing mistakes.
- **Dependencies:** [P4.2].
- **Acceptance criteria:** Original payments are never edited or deleted; correction reason, actor, time, amount, and linked payment are retained; invoice status reflects corrections.

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Source: MASTERPLAN.md — [P4.3]

MVP consolidation: Supersedes [P4.5], [P4.6] from the pre-trim plan.

Guardrails: Follow PROJECT_CONTEXT.md, keep Supabase queries and business logic in src/services/, use generated types, and preserve RLS on every exposed table.

Read PROJECT_CONTEXT.md and the P4.2 dependency first, then inspect the existing services under src/services and the generated types. Trace the current payment and invoice flows before defining the correction path; done means corrections retain their reason, actor, time, amount, and linked payment, leave original payments unchanged, update invoice status, and preserve RLS.

Written by the indexing model from the issue text.