docs: simplify CI/CD guides to 3-step pipeline

All three guides (vitest, xUnit, viewer) now follow the same
clear pattern: run tests → export HTML → copy to destination.

Removed overengineered content (REST API polling, health checks,
viewer-as-a-service). Kept genuine CI gotchas (allowOnly,
fileParallelism, build config mismatch, cross-platform httpyac).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dotnetprofessional