Migrate and expand Semaphore integration test suite

[dantro86]

Summary

• merge the existing Semaphore test automation history into the official integration-tests repository without squashing it
• preserve the repository-owned Bash output regression and Cloudflare R2/Worker infrastructure
• expand API, security, task lifecycle, runner, UI, configuration, and upgrade coverage
• keep scenario data in focused typed fixtures, including a dedicated SemaphoreShellOutputFixtures
• add a separate read-only externalTest task for user-managed Semaphore installations
• make the background-child output regression reliable on both local and persistent runners

The repositories share commit 531b7c0, so this PR uses a regular Git merge rather than copying the current tree. The official repository's seven unique commits and the legacy suite's thirteen unique commits remain reachable in history.

Validation

• ./gradlew --no-daemon qualityGate — passed
• scripts/run-external-tests.sh --no-daemon against a local Semaphore stand — 2 passed
• core API suite exercised on SQLite, PostgreSQL, MySQL, MariaDB, and PostgreSQL with a persistent runner
• persistent runner registration, health, routing, lifecycle, and security scenarios passed
• SQLite v2.19.7 -> v2.19.8 seed and verify phases passed
• PostgreSQL v2.19.7 -> v2.19.8 seed and verify phases passed
• runner-safe background-child regression passed after increasing the child lifetime to 60 seconds and keeping the completion limit at 30 seconds

GitHub Actions evidence

• PR CI — framework quality gate and Allure HTML artifact passed; the SQLite suite is red only on the task-output regression described below
• configuration matrix — TOTP, Git over HTTPS, encryption rotation, OIDC, proxy + OIDC, and the production PostgreSQL/persistent-runner profile passed; database/SSH/LDAP failures all contain the same missing-stdout signature
• release upgrade — SQLite and PostgreSQL reached the post-upgrade suite after successful seed/verify phases; Allure HTML artifact passed and the post-upgrade failure is limited to the same task-output regression

Known product failure

The pinned stable release images can lose short or early task stdout. This directly fails ShellOutputTest and can also hide output markers used by task-stop, Git, and SSH diagnostic assertions. The affected reports consistently show a successful task/fixture setup with stdout missing from the API response; configuration startup, authentication, database, runner, OIDC, Git HTTPS, TOTP, and encryption flows are otherwise healthy.

The product fix was merged in semaphoreui/semaphore#4159, but it is not included in the latest stable release (v2.19.12). The published semaphoreui/semaphore:develop image is currently an old 2-16-stable build, so it cannot be used as a reliable replacement. The regression assertions are intentionally not disabled or weakened.

Existing PRs

• Simplifies local integration-test development #2 can be rebased after this migration; its local fixture repository and Ansible working-directory coverage remain a separate concern.
• External #3 overlaps the new external test layer. Its Docker runner and report publishing pieces should be reviewed and moved separately instead of merging the whole branch into this migration.