Adopt living ADR lifecycle

[NWarila]

Summary

• [G-1, D-1, D-2, plan §5.7] Updates platform ADR-0001 in place to adopt the living-ADR lifecycle for the nwarila-platform control plane.
• [G-1, plan §5.7] Updates docs/decision-records/README.md with the lifecycle, editing decision tree, metadata expectations, and worked example.
• [Plan §5.6, DONE-INFERRED] Adds tools/check_adr_schema.py; live main did not contain an ADR schema checker to extend, so this PR adds the first one.
• [Plan §5.6] Wires the ADR schema check into self-ci.yml.
• [D-8, DONE-INFERRED] Refreshes ADR-0005 metadata while removing existing attribution residue from the platform control-plane ADR set.

Status

• DONE-VERIFIED: nwarila-platform/.github main had ADRs 0001-0005 and no existing tools/check_adr_schema.py before this branch.
• DONE-VERIFIED: ADR-0001 now demonstrates its own ## Changelog row.
• DONE-VERIFIED: platform control-plane ADR residue grep returns no matches after the ADR-0005 metadata refresh.
• DONE-INFERRED: The checker enforces living-schema requirements for changed ADRs while preserving unchanged pre-living ADRs until they are edited in their own PRs.

Validation

• ADR_SCHEMA_BASE_REF=origin/main python tools\check_adr_schema.py -> ADR schema check passed: 5 ADR(s), 2 changed ADR(s)
• python -m py_compile tools\check_adr_schema.py -> passed
• git diff --check -> passed
• python -c "<manifest source-existence check>" -> manifest: version=1, files=12; all sources resolve on disk
• residue grep for tool-attribution terms -> no matches