adr v1 (3/7): adr/v1 grammar as registered rule functions

[aaronsb]

Part of the ADR-304 rollout. Implement ADR-304 §1-§7, §11 and §12 rules, active only under contract: adr/v1:

• the kind schema read from adr.yaml
• verbs and capabilities
• the basis chain
• enactment
• typed amends/extends edges
• the vocabulary-layer check
• agent, considered and concern fields
• the Summary section with probes and inversion

Each rule is a function in the registry.

Done when: golden and negative fixtures pass for each rule, and the v0 goldens still pass.

[aaronsb]

Split into three PRs at the operator's request, each with its own fixtures and operator review:

• 562a: contract loading, the kind schema, verbs, capabilities, typed edges (supersedes/amends/extends/decided_by), change-must-supersede-or-amend, retire targets, config rules, the v0 count
• 562b: basis chains (must leave the corpus), operator levels, agent, considered, concern
• 562c: enactment (enacted: warn-then-fail over citations and inventories), the Summary with probes and inversion, the vocabulary-layer check on adr.yaml

This issue closes with 562c.