feat(balances): persist subentry count

[aditya1702]

Summary

Persist the account subentry count end-to-end so the Freighter v2 balances API can surface the v1 subentry_count field (part of the v1→v2 balances migration).

account.NumSubEntries was read in the accounts processor only to compute MinimumBalance, then discarded. It is now persisted:

• Schema: new num_subentries INTEGER NOT NULL DEFAULT 0 on native_balances (added to the existing CREATE TABLE — the DB re-migrates from scratch, pre-prod).
• Ingestion: carried on AccountChange, written via both the live-ingest BatchUpsert (UNNEST + ON CONFLICT) and the checkpoint BatchCopy paths.
• API/SDK: exposed as NativeBalance.numSubentries: UInt32! (GraphQL) and NativeBalance.NumSubentries (wbclient SDK).

The MinimumBalance formula is unchanged.

Testing

• make check — clean (0 lint issues, no deadcode, gql-validate passes).
• make unit-test (race) — full suite green, incl. DB-backed native_balances model tests via dbtest.
• Added coverage: num_subentries round-trips through GetByAccount/BatchUpsert/BatchCopy; buildAccountChange sets NumSubEntries; buildNativeBalanceFromDB sets numSubentries.

GraphQL generated code was regenerated via make gql-generate (not hand-edited).

Closes #651

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[Copilot]

Pull request overview

This PR extends the balances data model and API surface to support the v1→v2 balances migration by (1) persisting and exposing native numSubentries, and (2) exposing SAC token name/symbol sourced from contract_tokens.

Changes:

• Persist num_subentries for native balances through ingestion, checkpoint population, storage, GraphQL, and the wbclient SDK.
• Expose SAC name and symbol via the data read path, GraphQL, and the wbclient SDK.
• Add/extend unit tests to validate the new round-trips and resolver mappings.

Reviewed changes

Copilot reviewed 14 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/wbclient/types/types.go	Adds NumSubentries to native balance and Name/Symbol to SAC balance SDK types.
internal/services/token_ingestion.go	Carries NumSubEntries from indexer changes into native balance upserts.
internal/services/checkpoint.go	Persists NumSubEntries during checkpoint-based population into native balances.
internal/serve/graphql/schema/balances.graphqls	Adds numSubentries to NativeBalance and name/symbol to SACBalance in the GraphQL schema.
internal/serve/graphql/resolvers/account_balances_utils.go	Maps DB models to GraphQL models for new native/SAC fields.
internal/serve/graphql/resolvers/account_balances_utils_test.go	Adds resolver unit tests for numSubentries, name, and symbol.
internal/serve/graphql/generated/models_gen.go	Regenerates GraphQL models to include new fields.
internal/serve/graphql/generated/generated.go	Regenerates GraphQL execution code to include new fields and complexity hooks.
internal/indexer/types/types.go	Adds NumSubEntries to AccountChange for ingestion propagation.
internal/indexer/processors/accounts.go	Sets AccountChange.NumSubEntries from ledger account entry.
internal/indexer/processors/accounts_test.go	Adds test ensuring NumSubEntries is persisted through account processing.
internal/db/migrations/2026-01-15.0-native_balances.sql	Adds num_subentries column to the native balances schema definition.
internal/data/sac_balances.go	Extends SAC balance query/model to include ct.name and ct.symbol.
internal/data/sac_balances_test.go	Adds coverage for populated vs NULL SAC name/symbol.
internal/data/native_balances.go	Extends native balance model queries and write paths to include num_subentries.
internal/data/native_balances_test.go	Adds coverage for num_subentries in GetByAccount/BatchUpsert/BatchCopy.

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