feat: PostgreSQL driver support

docs/architecture.md

@@ -82,7 +82,7 @@ Uploaded images are addressed by a stored name (`<uuid>.<ext>`). `CreateImageUse
 
 SQL in repositories must run on SQLite, MySQL/MariaDB and PostgreSQL: substring searches use `LIKE ... ESCAPE '!'` through `containsPattern` instead of `instr`. `Settings.DataDir()` is where update state, staging and backups live; it is `DATA_DIR` when set and the directory of `DB_FILE` otherwise, so it does not depend on where the database is.
 
-Two drivers are registered in `database.drivers`: `sqlite` (default) and `mysql` (MySQL 8 and MariaDB 11, through `gorm.io/driver/mysql`, pure Go so `CGO_ENABLED=0` and the six release targets still build). `DB_DRIVER` picks one in `databaseConfig` (composition root); an unknown name fails in `database.Connect` with `unsupported database driver "<name>"`. `database.MySQLDSN` builds the DSN from separate variables, and the driver redacts the password from every error and names only host and port. `Connect` applies the optional `PoolSettings` to any driver. What keeps the repositories identical on both engines, all without touching the domain, use cases or handlers:
+Three drivers are registered in `database.drivers`: `sqlite` (default), `mysql` (MySQL 8 and MariaDB 11, through `gorm.io/driver/mysql`) and `postgres` (PostgreSQL 16 and 17, alias `postgresql`, through `gorm.io/driver/postgres` on pgx v5); all are pure Go so `CGO_ENABLED=0` and the six release targets still build. `DB_DRIVER` picks one in `databaseConfig` (composition root); an unknown name fails in `database.Connect` with `unsupported database driver "<name>"`. `database.MySQLDSN` and `database.PostgresDSN` build the DSN from separate variables (the PostgreSQL one as an escaped URL with `sslmode`, `timezone=UTC` and a connect timeout), and the driver redacts the password from every error and names only host and port. `Connect` applies the optional `PoolSettings` to any driver. What keeps the repositories identical on both engines, all without touching the domain, use cases or handlers:
 
 - Indexed and unique strings carry `size:` tags in the models (a MySQL index needs a bounded `varchar`). SQLite maps them to the same `text` column, so an existing SQLite file migrates with no schema or row change (`test/sqlite_schema_unchanged_test.go` builds a file from the old model definitions and compares `sqlite_master` and every row).
 - `Migrate` creates MySQL tables with `utf8mb4_bin` (`gorm:table_options`), so `Bob` and `bob` are distinct like in SQLite. The DSN also sets `collation=utf8mb4_bin`.
@@ -90,9 +90,11 @@ Two drivers are registered in `database.drivers`: `sqlite` (default) and `mysql`
 - The Go driver sends a zero `time.Time` as `0000-00-00`, which MySQL's default `NO_ZERO_DATE` rejects, so each session sets `sql_mode` to the server default minus `NO_ZERO_DATE`. Reading `0000-00-00` gives the zero time back.
 - `UserRepository.Create` returns the filled model instead of re-reading it, because MySQL has no `RETURNING`.
 
-Backups are a `domain/update.DatabaseBackup` per driver. SQLite uses `VACUUM INTO`. MySQL uses `DumpBackup`, a pure Go logical dump (`SHOW CREATE TABLE` plus every row, strings escaped and binary values as hex, NULL and zero dates kept) written inside one repeatable-read transaction to `DATA_DIR/backups/renewcms-<time>.sql.partial` and renamed once complete. Any failure removes the partial file and returns an error, so the update download fails instead of claiming a backup. Both keep the newest 3 files (`pruneBackups`).
+On PostgreSQL the MySQL-only table options are not applied, pgx returns `timestamptz` values in the local zone so a query callback in the driver converts them to UTC, and only the `public` schema is used.
 
-`task test` runs everything that needs no server. The repository contract tests (`test/repository_contract_test.go`) run on SQLite always, and on MySQL when `RENEWCMS_TEST_MYSQL_DSN` points at a server (admin DSN; each test creates and drops its own database). `task test:mysql` starts `mysql:8.4` and then `mariadb:11` in Docker and runs the `MySQL` tests against each.
+Backups are a `domain/update.DatabaseBackup` per driver. SQLite uses `VACUUM INTO`. MySQL uses `DumpBackup`, a pure Go logical dump (`SHOW CREATE TABLE` plus every row, strings escaped and binary values as hex, NULL and zero dates kept) written inside one repeatable-read transaction to `DATA_DIR/backups/renewcms-<time>.sql.partial` and renamed once complete. Any failure removes the partial file and returns an error, so the update download fails instead of claiming a backup. PostgreSQL reuses `DumpBackup` with its own `dumpDialect` (double-quoted identifiers, doubled single quotes, `\x` bytea literals): `CREATE TABLE` is rebuilt from `pg_catalog` (serial columns, defaults, primary key, unique and check constraints), followed by the indexes, the rows and a `setval` per `id` sequence, all inside one repeatable-read read-only transaction. All drivers keep the newest 3 files (`pruneBackups`).
+
+`task test` runs everything that needs no server. The repository contract tests (`test/repository_contract_test.go`) run on SQLite always, and on MySQL when `RENEWCMS_TEST_MYSQL_DSN` points at a server (admin DSN; each test creates and drops its own database). `task test:mysql` starts `mysql:8.4` and then `mariadb:11` in Docker and runs the `MySQL` tests against each. The same contract tests run on PostgreSQL when `RENEWCMS_TEST_POSTGRES_DSN` points at a server (admin DSN, for example `postgres://postgres:pw@127.0.0.1:5432/postgres?sslmode=disable`), and `task test:postgres` starts `postgres:16` then `postgres:17` in Docker and runs the `Postgres` tests against each.
 
 Two storage adapters implement `image.Storage`: `local` (default, files in `UPLOAD_DIR`) and `s3` (`storage.S3Storage`, `aws-sdk-go-v2` over plain HTTPS, pure Go so `CGO_ENABLED=0` still holds). `STORAGE_DRIVER` picks one in `imageStorageConfig` (composition root, from `config.StorageSettings`); `storage.Open` fails with `unsupported storage driver "<name>"` for anything else, and `openImageStorage` panics with the error. The S3 adapter works as follows, with no change to the domain, use cases, repositories or the `staticimages` handler: