Add ISO26262 verification report schema tree (no generator yet)

[FScholPer]

Context

Schema-first foundation for verification report sections.

Scope

Add three schema files only:

• scripts_bazel/verification_report_schema.json
• scripts_bazel/verification_coverage_schema.json
• scripts_bazel/verification_evidence_schema.json

Out of scope

• generation logic
• template rendering
• CI gate enforcement updates

Acceptance criteria

• files exist
• JSON is valid
• top-level schema references traceability schema