tests(api): add budget report/progress Decimal serialization contract (ignored until budget Decimal migration)

[zensgit]

Purpose / Problem

• Lock JSON contract: all budget money fields serialize as string; percentage fields remain numeric.
• Test is marked #[ignore] until budget Decimal migration lands, so it won’t affect CI now.

Summary of Approach

• Add test file only: jive-api/tests/contract_decimal_budget.rs.
• Mirrors pattern of merged serialization contract tests for market/account/transactions.
• Validates:
  • BudgetProgress: budgeted_amount, spent_amount, remaining_amount → string
  • BudgetReport: total_budgeted, total_spent, total_remaining, unbudgeted_spending → string
  • BudgetSummary: budgeted, spent, remaining → string
  • Numeric: percentage_used, overall_percentage, BudgetSummary.percentage
• No business logic changes.

Testing Evidence

• Local build with SQLX offline:
  • SQLX_OFFLINE=true cargo test --no-run → ok (tests compile; new test is ignored)
  • SQLX_OFFLINE=true cargo clippy -D warnings → ok (no issues related to this change)

Migration Notes

• None for DB/schema. When migrating budget to Decimal:
  • Move f64 money fields to Decimal and ensure serde as string (consistent with market/account/transaction).
  • Remove #[ignore] on this test to enforce contract.

Rollback Plan

• Safe to revert by removing the new test file if needed; no code paths touched.

Related Context

• Follow-ups to merged decimalization work: api: migrate transaction/budget money types to Decimal #90, api: migrate exchange rate & market to Decimal #92, tests: add Decimal serialization contract tests #93, api: migrate Transaction model/service to Decimal #94.

Checklist

• Adds test-only change; CI unaffected now
• Matches crate path: jive_money_api
• No API or handler logic change
• Remove #[ignore] immediately after budget Decimal migration lands
• Verify Flutter client continues parsing money as string for budget endpoints
• Add rounding/formatting edge-case tests post-migration

[zensgit]

Re-triggered CI by pushing a no-op commit.

• This PR is test-only and marked #[ignore], so CI should remain green.
• Once checks pass, I'll auto-merge to chore/invitations-audit-align-dev-mock.

Post-merge follow-ups (recommendation):

• Migrate budget money fields to Decimal with string serialization parity.
• Remove #[ignore] in contract_decimal_budget.rs to enforce the contract.
• Update Flutter budget parsing to accept money as string (consistent across modules).
• Add rounding/format edge-case tests in a follow-up PR.

[Copilot]

Pull Request Overview

Adds an ignored test to lock the JSON serialization contract for budget endpoints: money fields should serialize as strings and percentage fields remain numeric.

• Introduces jive-api/tests/contract_decimal_budget.rs with a comprehensive serialization contract test.
• Asserts string serialization for key money fields; asserts numeric serialization for percentage fields.
• Test is #[ignore] pending the Decimal migration for budget models.

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[Copilot]

[nitpick] val is shadowed later (see line 57) when serializing the report, which slightly reduces clarity. Consider renaming to progress_json and report_json to make the two JSON values distinct.