Multi-currency: FX conversion and reporting currency - #56

…ency across read paths

Move the service-layer legacy snapshot resolution out of the FX-wiring
commit. Every read path (expense list, detail, correction history,
pro-rata group, and export stream) resolves repository-synthesized
legacy rows to the period reporting currency and emits normalization
telemetry, without failing the read when period context is unavailable.

…mount sort and currency filters

- gofmt suggestions model/service files
- rename misleading legacy-suggestion test
- name and document the reporting-currency fallback
- label dual amounts as budget impact for accessibility
- scope mobile mixed-currency test to the mobile list
- make canonical suggestion fields optional so fallbacks are meaningful
- add foreign-suggestion-currency integration test

…er review-11

…l work

- Collapse mapFxError to a single safe CONVERSION_UNAVAILABLE mapping; the
  dead gRPC-code switch implied distinctions that do not exist.
- Normalize the period reporting currency once in CreateExpense and use it
  for validation, the identity-vs-FX decision, snapshots, and the FX target.
- Require a non-nil FxClient: NewExpenseService panics on nil instead of
  leaking a test-only runtime fallback; tests use a loud stubFxClient.
- Return and close the FX gRPC connection in main.go, matching the finance
  client pattern.
- Drop unused FxConvertResponse echo fields and use the shared exchange
  source constant in tests.
- Assert RequestedAt in FX success tests via a fixed clock seam.

Spec 05 requires Expense to preserve FX error categories rather than
collapse every gRPC status into 503. mapFxError now inspects status.Code:

- Unavailable/FailedPrecondition -> 503 CONVERSION_UNAVAILABLE
- InvalidArgument UNSUPPORTED_CURRENCY -> 400 UNSUPPORTED_CURRENCY
- InvalidArgument INVALID_AMOUNT -> 400 VALIDATION_ERROR
- Internal/unclassified -> 500 INTERNAL_SERVER_ERROR (reported)
- non-gRPC transport failure -> 503 CONVERSION_UNAVAILABLE

Also address review-7 nits: report an unsupported period reporting
currency as a 500 internal invariant violation (not a retryable 503),
rename the misnamed FX-client-unavailable test, and replace the
always-true repo matcher with mock.AnythingOfType.

…g currency first

- Log non-503 FX failures (Internal/unclassified) as Error with event
  foreign_currency_conversion_failed instead of the misleading
  foreign_currency_conversion_unavailable Info event.
- Validate the period reporting currency before resolving the transaction
  currency so a corrupted reporting currency surfaces as a 500 internal
  invariant violation in every branch, including the no-currency-fields
  defaulting path, instead of a 400 transaction-currency error.
- Add tests for both behaviors.

- Remove LegacySynthesized/PartialSnapshotFields and service-layer legacy normalization; rely on InitSchema backfill and version-0 error.
- Read suggestion transaction columns directly without the legacy amount/currency fallback; keep version-1 integrity telemetry.
- Update finance tests for the removed reporting-amount fallback and read the shared currency catalog from code.

- Make transactionAmount, reportingAmount, and reportingCurrency required and read them directly without legacy fallbacks.
- Update finance and shell fixtures/mocks to supply the required snapshot fields.
- Fix shell mock reporting-currency fields for comparison, health score, and trends.

…ntegrity telemetry

… column drop

…arison logic

…ount/transaction_currency

… period states

… states

… comment

The suggestions API no longer returns the deprecated amount/currency
aliases, so the autocomplete smoke test asserts transactionAmount.