[DB] Use Postgres startup encoding without SET NAMES

[kageiit]

Postgres encoding uses the startup packet.
The patched tokio-postgres driver already requests UTF8 when connecting. Quaint repeated it with SET NAMES on every connection, causing all 9,946 RDS Proxy warnings in the production window to report session pinning. Remove the redundant SQL and retain explicit schema initialization.

Validation: local PostgreSQL 17 tests pass for UTF-8 round trips and custom search paths. Formatting passes. All-target clippy completes with the existing approximate-constant test lint allowed, retaining unrelated warnings.

Gitar needs a separate consumer version-pin PR. Existing sessions remain pinned until they reconnect after deployment.

Fork pull requests now run the supported Postgres compatibility workflow, including the encoding and search-path regressions against PostgreSQL 17. The upstream main branch retains its original multi-connector workflow.

Decisions made while unattended

• Scoped fork CI to its supported Postgres contract as the upstream matrix fails deprecated actions and unrelated warning baselines
• Added the encoding regressions beside the existing TLS checks so the narrower workflow still exercises this change