Strengthen repository prose audits

[owieschon]

Problem

Sourcebound could classify repository prose and common package surfaces, but its PR verdict returned unknown for a comment-only Makefile edit. The same change set also exposed gaps in context pinning, optional proposer containment, and machine-readable advisory output.

Changes

• expand repository-neutral prose and corpus checks without turning the bundled register into universal policy
• pin context compilation to committed request bytes and source evidence
• contain the optional init proposer and publish complete machine advisory occurrences
• add a bounded static Makefile adapter for targets, referenced assignments, recipes, and phony state
• fail closed on dynamic Make syntax, orphan recipes, unexplained semantic residue, and partially classified changes
• version the inventory cache contract and update canonical documentation and projections

Test plan

• 679 tests passed
• Ruff passed
• mypy passed across 60 source files
• Sourcebound check, audit, verify, and trusted self-check passed
• self-audit reported zero findings and zero advisories
• the original ultra-csm PR now produces a ready verdict with zero unknown impact findings
• four independent adversarial reviews approved the final adapter boundary