feat(conformance): add normative clause inventory (021)

[pofallon]

Summary

Adds the normative clause inventory (feature 021) — the prose companion to the schema constraint inventory (020). A machine-canonicalized inventory of every normative clause in the 18 ratified upstream devcontainers/spec prose documents (pinned at 113500f4), classified under deacon's consumer-only scope, with move-aware drift detection and a certify gate. No LLM or network in any CI-facing command.

What's included

• Vendored pinned prose under conformance/spec/113500f4/ (14 consumer + 4 authoring docs) with a SHA-256-fingerprinted manifest.json; re-vendored only on a pin bump.
• Machine-owned conformance/inventory/clauses.json (clu- units, substance-anchored ids: hash8 over document ‖ normalize_substance, location excluded so a pure move keeps its id/disposition).
• Hand-authored clc- classifications: per-clause for consumer docs, document-scope not-applicable defaults for authoring docs, plus per-clause behavior-mapped overrides for the consumer install/apply clauses inside features/templates.
• New prose model: deterministic ATX heading reader, substance normalizer, RFC-2119 strength detection.
• New CLI subcommands (dev-only deacon-conformance): clause generate / check / diff / scaffold.
• Validation: V11–V14 generalized from constraint units to inventory units; new V15 clause↔source integrity. Clause join wired into validate, certify, and report.
• Source retirement: three redundant src-spec-* prose source units retired now that their behaviors back-trace through behavior-mapped clause classifications.

Notes

• Includes a fix to clause diff's pair_changed: a removed + added clause under a shared heading are paired into a changed entry only on an unambiguous 1:1 match; multi-clause headings are left as distinct removed/new entries rather than mispaired (which would fabricate a spurious rewrite and hide genuine add/removes). Regression test added.

Verification (local, hermetic)

• cargo fmt --all -- --check clean; cargo clippy --all-targets --all-features -D warnings clean.
• deacon-conformance suite: 261/261 passing.
• clause check byte-identical regeneration; validate clean; certify clean (0 blocking, 10 waived).

The parity / live-certification lane is not in scope here (dev-only-crate change; needs Docker + the pinned oracle, which don't run in the authoring workspace).

🤖 Generated with Claude Code

https://claude.ai/code/session_019vhr7Tcf8ybvSZSE1owqBT