[DR-002-Proc] Implement FEP process

### Epic Description

Tracking issue for the implementation of DR-002-Proc (Feature & Enhancement Proposal process) after acceptance.

This issue remains open until all implementation tasks below are merged.

### Acceptance Criteria (DoD)

- [x] [Feature Request Guideline](https://eclipse-score.github.io/score/main/contribute/contribution_request/feature_request.html): Add routing decision at entry; platform/cross-FT FRs → FEP process, single-FT FRs → FT authority
- [x] [Project Management Plan](https://eclipse-score.github.io/score/main/platform_management_plan/project_management.html): Correct formal error: PMP assigns FR review to TL circle; update to reflect Architecture Community ownership for platform/cross-FT FRs, TL role → triage
- [x] [Change Management Plan](https://eclipse-score.github.io/score/main/platform_management_plan/change_management.html): Add two-tier taxonomy; map FEP acceptance to existing Change Request status flow
- [x] [Software Architecture Overview](https://eclipse-score.github.io/score/main/users_guide/project_basics/software_architecture_overview.html): Update reference to FEP process for structural/platform-level changes
- [x] [Process Description - Change Management](https://eclipse-score.github.io/process_description/main/process_areas/change_management/index.html) | No change required; FEP Shepherd + FCP implements `wf__change_analyze_cr` for platform-level FRs
- [x] Open Feature Requests are on-boarded to the new FEP Process

Review the linked Feature Request Guideline, Project Management Plan, Change Management Plan, Software Architecture Overview, and process description pages. Verify that the checked documentation updates and open Feature Request onboarding are present in the referenced locations; done means all listed acceptance criteria are merged and the tracking issue can close.

Written by the indexing model from the issue text.