Drop the pooler from the MVP: point everything straight at Postgres

.env.example and the README still told people to use pgCat on :6432, the
exact setup that hangs on every parameterised query. With no prod and one
backend instance there is nothing for a pooler to multiplex, and
postgres-js already pools in-process, so DATABASE_URL now points at
Postgres on :5432 in .env.example, dev-env.sh and drizzle.config.ts.

prepare:false is kept in src/db/index.ts on purpose, so adding
PgBouncer later (tested working) is a config change rather than a code
change. The long measurement narrative in that file's comment is cut to
the decision and the pointer to PLAN.md, where the numbers now live.

README.md

@@ -1,7 +1,6 @@
 # continuum-backend
 
-Cloud control plane for Continuum. Bun + ElysiaJS, PostgreSQL (via pgCat/PgBouncer,
-with pgvector for frame embeddings), Valkey Streams, and Cloudflare R2 storage.
+Cloud control plane for Continuum. Bun + ElysiaJS, PostgreSQL (with pgvector for frame embeddings), Valkey Streams, and Cloudflare R2 storage.
 
 ## Run
 
@@ -48,7 +47,7 @@ backend and records what a gateway sends, for refreshing the fixtures in
 ## Layout
 
 - `src/db/` - Drizzle schema (`printers`, `farms`, `print_jobs`, `frame_embeddings`)
-  and client, pointed at pgCat. `src/db/validators.ts` derives Elysia/TypeBox
+  and client, pointed straight at Postgres. `src/db/validators.ts` derives Elysia/TypeBox
   request validators straight from the Drizzle tables via `drizzle-typebox`,
   so the Postgres schema and the API validators come from one definition
   instead of two hand-synced ones.