Add initial Robot Framework public smoke tests

[khorovatin]

Summary

This PR adds an initial Robot Framework smoke test scaffold for the public Spaceport portal.

Included

• .gitignore coverage for generated test artifacts
• shared Browser-based Robot helpers
• landing page page-object resource
• public messaging page-object resource
• initial smoke suite for public landing-page rendering and basic public navigation
• README and requirements for local setup

Verified

Ran successfully from repo root with:

robot -d results tests/robot/tests/smoke.robot

Not included

This PR intentionally excludes:

• login-specific page objects
• broader regression or authenticated workflows