Enforce evidence authorship and attestation semantics

[maximalfocus]

Closes #107

Outcome

• adds immutable dossier schema v2 with normalized evidence authorship and accountable-person attestation while preserving schema v1
• blocks unattested assistant-authored observations and estimates across the centralized credible-evidence boundary
• records effective authorship in schema-v2 decision records and classifies attestation reassessment causes explicitly
• advances the public method to 1.4.0 and ruleset to 1.10.0 while preserving the 1.3.0/1.9.0 review binding

Verification

• 1,181 tests passed
• Ruff format/check passed
• strict mypy passed
• 500-evidence benchmark: 0.274s <= 2.0s
• sdist and wheel built; installed-wheel schema-v2 validate/assess smoke passed without dependency resolution