score::time::SystemTime: Create SW component requirements and establish traceability

`score::time::SystemTime` has no SW component requirements defined.
Requirements shall be authored as sphinx-needs `comp_req` directives,
traced up to the corresponding feature requirements in the central `score/`
repo, and traced to implementing code via `// # req-Id:` comments.

**Location**
Requirements RST file shall be created at:
`score/time/docs/requirements/system_time_requirements.rst`

**Requirement format**
```rst
.. comp_req::
:id: comp_req__time__system_time_<keyword>
:status: draft
:safety: QM
:satisfies: feat_req__time__<feature_req_id>
```

> **Note:** `feat_req` nodes live in the central `score/` repository and are **not** resolved by the local `bazel build //:docs`. The `:satisfies:` field must still be set to the correct UID — traceability validity is verified by the central CI pipeline that has access to the full `needs.json`.

**Acceptance Criteria**
- [ ] `score/time/docs/requirements/system_time_requirements.rst` created and included in the component docs index
- [ ] All significant observable behaviours of `score::time::SystemTime` are captured as `comp_req` nodes
- [ ] Every `comp_req` node has a `:satisfies:` field referencing a valid `feat_req` UID from the central `score/` repository
- [ ] Every `comp_req` node is traced to at least one implementing code location via `// # req-Id:`