ci: verify docs, examples, Docker artifacts, and upgrade paths

[RatulMaharaj]

Problem

Unit tests are strong, but CI does not fully verify that documentation links resolve, every example validates, generated deployment shapes boot, or a release upgrade preserves agent data.

Scope

• Add internal documentation-link validation.
• Validate every example agent config in CI.
• Build and smoke-test the base image and representative custom images.
• Add container boot tests for health, webhook, and status authentication.
• Add database and config migration fixtures across supported releases.
• Add release smoke checks before publish workflows run.
• Report coverage and integration-test results without making coverage percentage the only quality signal.

Acceptance criteria

A merged change cannot silently break a documented command, example, release image, or supported data/config upgrade path.