os: define requirements and clean up test-to-requirement traceability

## Goal

Define the missing component requirements and architecture for the OS component (`score/os/`), then apply the test-to-requirement traceability cleanup described in #522.

## Requirements and architecture

Create the requirements and architecture documentation below `score/os/docs/`. The prior documentation path recorded in this issue is obsolete.

Requirements shall describe the current observable behavior of the OS wrapper families and be allocated to the OS component architecture with valid upstream feature traceability. Do not use a generic requirement solely to attach every OS test. Do not create artificial tests for structural requirements that are verifiable only by inspection.

## Test-to-requirement traceability

Review every C++ gtest under `score/os/` against the new `comp_req__os__...` needs. Replace legacy `Verifies` links to `SCR-46010294` and `SCR-109773` with mandated `FullyVerifies` or `PartiallyVerifies` links to the requirements genuinely exercised by each test.

Record the mandated `TestType`, `DerivationTechnique`, and self-contained `Description` metadata for linked tests. Remove legacy `ASIL` properties and normalize invalid derivation values such as `equivalence classes` to `equivalence-classes`.

## Scope boundary

Cover the current OS component baseline without duplicating separate feature work, including #501, #527, and #72 through #76.