Add in-repo SQA testing plan/cases/results documentation for release process

[Copilot]

artdaq needs explicit SQA artifacts for a Moderate SQA level: an appropriate test plan, defined test cases, and documented test results expectations per release. This PR adds those artifacts in-repo and links them from the main project entry point.

• SQA documentation added

  • New doc/SQA_Testing.rst defines:
    • testing scope and SQA intent
    • 3-tier test plan (unit/component, artdaq-demo acceptance, experiment-environment acceptance)
    • minimum release test case groups
    • required per-release test result record fields (release ID, environment, pass/fail by group, exceptions)

• Discoverability update

  • README.md now points to doc/SQA_Testing.rst so contributors and release coordinators can locate SQA testing guidance quickly.

• Example (new release record expectations)

  * Release identifier (version/tag/commit range).
  * Date and responsible tester(s).
  * Environment summary (platform/container/toolchain).
  * Test case groups executed.
  * Pass/fail result for each executed group.
  * Notes for failures, waivers, or follow-up actions.