ux(postgres): hint to enable SSL when the server rejects the connection with "no encryption" #1754

Problem

A server whose `pg_hba.conf` only allows `hostssl` answers a plain connection with:

```
28000: pg_hba.conf rejects connection for host "10.10.0.129", user "...", database "demo", no encryption
```

Querya shows this raw text in the Test connection result. The cause (SSL is off in the form) is not obvious: it reads like wrong credentials or an IP block. Seen while connecting to startde.postgres.karpov.courses; ticking SSL is the fix.

Proposal

• When a Postgres connect error is a `pg_hba.conf rejects connection` containing `no encryption`, append a hint to the message: "The server requires an encrypted connection. Enable SSL and try again."
• In the connection form, offer a one-click "Enable SSL and retry" next to that Test result.
• Keep the raw server message visible (do not hide it behind the hint).
• Optional follow-up: an `sslmode=prefer`-style fallback (try plain, then TLS) when the URI has no explicit `sslmode`.

Where

• `lib/core/database/postgres_connection.dart` (`_connectOnce` catch, `describeDatabaseError`)
• `lib/features/postgresql/postgresql_connection_form.dart` (`_testConnection`, `_showTestResult`)

Notes

The connect attempt and its raw error are now logged with `debugPrint` (no password), which is how this was diagnosed.