fix: dial scenario PGWire directly with SNI

[bill-ph]

Summary

• separate the managed-hostname TLS/SNI identity from the direct PGWire TCP dial address
• use a lib/pq connector dialer for both scenario SQL and perf PGWire clients instead of the unsupported DSN hostaddr setting
• retain dbt's numeric PGHOSTADDR behavior and document the explicit transport split

Root cause

The Go lib/pq driver resolves host for TCP dialing and does not implement libpq hostaddr semantics. The scenario hostname is intentionally not resolvable, so SQL and perf failed before reaching the control plane.

Validation

• go test -count=1 ./tests/mw-dev/scenario/... ./tests/mw-dev ./tests/perf/drivers/pgwire
• just lint

The direct-dial regression test uses an unresolvable SNI hostname and a local TCP listener, proving that the connection reaches the direct address while TLS still carries the expected SNI.

[github-actions]

Test Impact Plan

Deterministic summary of how this PR changes tests, CI runners, and coverage-risk signals.

Summary

Area	Added	Changed	Deleted
Test files	0	11	0
E2E/journey files	0	0	0
Workflow files	0	0	0

Signals

• Test cases: +3 / -2
• Assertions: +20 / -7
• Skips or known failures added: 0
• Workflow continue-on-error added: 0
• Workflow path filters added: 0
• Test commands removed from justfile: 0
• E2E/journey retry lines added: 0

Coverage risk: neutral or increased

No coverage-reduction warnings detected.