Adopt `bazel_platforms` as the single source of truth for build platforms

### Description
We need to standardize how build platforms are defined across the S-CORE ecosystem by using the [`eclipse-score/bazel_platforms`](https://github.com/eclipse-score/bazel_platforms) repository as the **single source of truth**.

#### Background
The `bazel_platforms` repository serves as the central definition hub for S-CORE Bazel platforms and constraints.
It is designed to:
- Provide global constraints that complement Bazel’s standard set, enabling more precise environment description and selection.
- Define consistent platform configurations to ensure seamless and uniform toolchain selection across all S-CORE modules.
- Promote compatibility, reproducibility, and clarity in build environment definitions.

#### Required actions
1. Identify all repositories currently defining local platforms (e.g., in `toolchains_qnx`, `toolchains_rust`, `module_template`, etc.).
2. Decouple those platform definitions from the toolchain repositories.
3. Reference the centralized `bazel_platforms` repository instead, using appropriate Bazel module dependencies or workspace overrides.
4. Update documentation and CI configurations to reflect the new platform source.