feat(budget): account_category filter and typed source_anomalies

[makegov-mark]

What

Support for the Tango API 5.7.0 and 5.8.0 budget-account contract changes: account_category, source_anomalies, and data_through_period (the File A fiscal period, 1–12, an account-year's figures run through; null with no File A data), read with BudgetDataThroughPeriod and filtered with DataThroughPeriod / Gte / Lte / IsNull.

• /api/budget/accounts/ now serves account_category (budgetary | credit_financing today, an open string) and source_anomalies (a list of source-data problems, [] when clean) in its default shape.
• ListBudgetAccountsOptions gains AccountCategory (account_category) and AccountCategoryIn (account_category__in, comma-joined).
• BudgetSourceAnomalies(row Record) ([]BudgetSourceAnomaly, error) decodes the list. BudgetSourceAnomaly, BudgetSourceAnomalySource and BudgetSourceAnomalyRow follow the SDK's typed-model pattern: every field optional (pointer or slice), unknown keys in Extra. It returns nil when the key is absent or null and an empty slice when the row is clean.
• Constants for today's categories (BudgetAccountCategory*) and anomaly codes (BudgetAnomaly*).
• ShapeBudgetAccountsMinimal now names account_category and source_anomalies, so a capped contract_obligated arrives with the anomaly explaining it.
• The API's default ordering now puts null enacted_ba last; documented, no code change needed. There is no anomaly filter.

Testing

• go vet ./... and go test -race ./... pass.
• New tests cover the filter mapping, a list response decoded through BudgetSourceAnomalies (full element, nested source rows, unknown keys in Extra, a clean [] row), absent/null keys, and a malformed value.
• golangci-lint: the locally installed v2 cannot read the repo's v1 config; run with a migrated copy, it reports only pre-existing findings and nothing in the changed lines. CI lint runs the repo's own config.

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