docs(configurator): explain reproducible manual UI releases

[lweberru]

Summary

Document the exact GitHub UI release flow requested by the user: Actions > Configurator Release > Run workflow > main > build_only=false > empty release_run_id, followed by the existing lzc-dev-release approval. Also explain build-only preparation, immutable-artifact promotion and first-attempt/branch-HEAD restrictions.

Evidence

• Development promotion run 38946918239 succeeded, including Runner isolation, migrations, service connectivity and public checks.
• Post-deployment live browser checks passed 3/3, including same-tab STACKIT login. Initial old-release observations and the test-only missing-Origin cleanup failure remain retained privately rather than overwritten.
• Full default fresh-release run 38949600367 is executing to verify qualification/build/tag creation as well as deployment; main must not advance until its HEAD-bound publication gate completes.

Documentation only; no application, infrastructure, permission or workflow changes.

[lweberru]

End-to-end validation completed: full default UI-equivalent release https://github.com/stackitcloud/stackit-landing-zone/actions/runs/38949600367 succeeded with all four jobs (real Assistant qualification, build, automatic protected-tag publication using GITHUB_TOKEN, deployment). Real-model suite 114/114 and continuous dialogue 13/13 passed. Direct read-only CF verification confirms current API and Runner droplets both use exact source dbac037. All three final live-browser journeys passed, including same-tab STACKIT login and unauthenticated tenant-resource protection. No production resources or customer Plan/Apply were changed. Historical failures remain recorded; no automatic deployment retries were added.