Unify local PostgreSQL port expectations across Docker and standalone setups

[tystar86]

Imported from Linear: TYS-162

Source: docs/developers/START_HERE.md → ## Common Pitfalls

Standalone local PostgreSQL uses host port 5432, while Docker exposes PostgreSQL on host port 5433. This is easy to miss during setup and troubleshooting.

Goal:

• Reduce onboarding friction caused by port mismatches.
• Decide whether the difference should be standardized, surfaced more clearly, or automated in local setup guidance.

Acceptance ideas:

• Local setup instructions make the port distinction obvious.
• Common connection errors caused by using the wrong port are easier to avoid.

[tystar86]

Closing — this work landed in PR #48 (TYS-162).