Wave 2 Onboarding for Toolchain and Platform Repositories

## Goal
Extend harness/policy rollout to toolchain and platform repositories.

## Why
Toolchain repos need language-specific validation while keeping the same governance contract.

## Scope
Target groups: `toolchains_*`, `rules_*`, `bazel_*`, `score_*_policies`, `score-crates` and related platform repos.

## Required Additions
- C++/Rust/Bazel specific validation stages (compile/lint/test/security checks where applicable).
- Adapter mapping from repo-specific outputs to common evidence schema.
- Language/toolchain-specific failure taxonomy for triage.

## Rollout Steps
1. Batch repositories by stack similarity.
2. Implement common template + stack-specific extensions.
3. Run soft-fail calibration window per batch.
4. Promote batch to hard-fail after stability criteria are met.

## Stability Criteria (per batch)
- Required Lane A checks pass reliably in CI.
- Artifact schema validation success is consistent.
- Policy decisions are reproducible within agreed tolerance window.
- No unresolved blocker in shared workflow layer.

## Done When
- Wave 2 repositories are onboarded in documented batches.
- Each batch has a published cutover decision (soft-fail -> hard-fail).
- Repo owners confirm branch protection checks are active.

Parent: https://github.com/eclipse-score/score/issues/2827