refactor(core): remove legacy account runtime schemas

[kitlangton]

What

Remove the dead Core Account runtime schemas while preserving the legacy SQLite account tables and all existing data. Current V2 authentication uses the Credential and Integration modules; no runtime code consumes the old Account login, polling, organization, token, or error schemas.

Before / After

Before: packages/core/src/account.ts exported 101 lines of unused runtime schemas. The legacy Drizzle table declarations depended on four branded types from that otherwise dead module.

After: The unused runtime module is gone. account, account_state, and control_account remain unchanged in the canonical schema and in existing databases; their declarations use ordinary SQLite string types instead of importing the deleted runtime namespace.

How

• Delete packages/core/src/account.ts.
• Keep packages/core/src/account/sql.ts as the legacy schema owner.
• Remove only TypeScript $type annotations that depended on the deleted Account namespace; these annotations do not alter SQLite schema generation.
• Confirm migration generation reports no schema changes.

Scope

• No tables, columns, rows, credentials, migrations, or generated schema artifacts are changed.
• This does not touch the unrelated Console Account schema or provider-specific account IDs.
• Removing the physical legacy tables can be considered separately later.

Testing

• bun run migration --check from packages/core: passed; no schema changes or migration generated.
• bun run test test/database-migration.test.ts test/credential.test.ts from packages/core: 9 passed, 0 failed.
• bun typecheck from packages/core: passed.
• Push hook bun turbo typecheck --concurrency=3: 33 tasks passed.