Add methodology subtype inventory

[pidongqianqian]

Closes #53.

This backfills the remaining methodology subtype gaps that were clear from the issue:

• tags the FedRAMP threat-based risk profiling methodology as scoring
• carries parent subtypes onto version/style child nodes for SSVC, CVSS, and NIST IR 8477
• adds an inventory doc showing all 56 methodology match nodes are now tagged
• records the current reference inventory: 236 reference match nodes, all intentionally left untagged for a dedicated glossary backfill decision
• extends scripts/validate-subtypes.py with recursive match_node scanning and optional --completeness warn|fail

I left the reference glossary backfill as a follow-up decision point in the inventory doc. It looks like a larger sweep and seemed better to keep separate from the obvious methodology cleanup.

Checks run:

• python3 scripts/validate-subtypes.py
• python3 scripts/validate-subtypes.py --completeness warn
• python3 -m json.tool on the four edited registry JSON files
• git diff --check