feat(pg-codegen): generated Prisma-like db client over query-builder

[pyramation]

Summary

pg-codegen output now includes a high-level database client mirroring the GraphQL ORM's surface, so consumers stop hand-assembling SELECT lists, columnByField lookups, and per-column decoder calls:

const db = createAgentDb(pool, { schema: agent.schema, tables: { agentThread: agent.threadTable } });

const thread = await db.agentThread.findFirst({
  where: { id: threadId },
  select: { id: true, model: true, systemPrompt: true, agentId: true }
}); // Pick<AgentThread, ...> | null — decoded, camelCase

const msg = await db.agentMessage.create({ data: { threadId, parts }, select: { id: true, createdAt: true } });
await db.agentTask.updateOrThrow({ where: { id, threadId }, data: { status } });

const txDb = db.$with(txClient); // rebind to a transaction's PoolClient

Two new emitted files:

• client.ts — shared runtime, copied from a typechecked template (src/emit/templates/client.ts, same pattern as graphql-codegen templates). TableClient<App> wraps @constructive-io/query-builder: findMany / findFirst / findFirstOrThrow / count / create / update / updateOrThrow / delete, camelCase where in the shared query-spec grammar (equalTo, in, greaterThan, startsWith, and/or/not; bare value = equalTo, null = isNull), select: { field: true } narrowing the result type via SelectResult, orderBy: { createdAt: 'DESC' }, rows decoded through the generated field decoders, writes serialized (Dates → ISO, json fields → stringify, arrays passed through to pg). Zero-row updateOrThrow/findFirstOrThrow throw RowNotFoundError — never silent.
• <schema>/db.ts — AST-emitted create<Schema>Db(db, options?) factory binding one TableClient per table over the existing <TABLE>_TABLE / <TABLE>_FIELDS constants, with runtime schema/per-table name overrides for tables provisioned into per-tenant schemas, plus $with for transactions.

Notes:

• pg-codegen gains a @constructive-io/query-builder dependency (generated output imports it); templates are copied into dist/ at build like graphql-codegen.
• Unlike the GraphQL ORM there is no .execute() envelope — pg errors throw, so methods are plain promises.
• New live round-trip suite (__tests__/client.test.ts) runs the committed fixture client against a provisioned DB: CRUD, projections, filter grammar, and/or/not, count, $with. 48 tests green.

Link to Devin session: https://app.devin.ai/sessions/b1fb8d90ec0a4cd1bd95e3c77c6f6680
Requested by: @pyramation

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