feat: add Elite Decision Protocol

[ernestprovo23]

What changed

• adds the quality-first elite council mode
• runs independent answers, claim audits, and revisions before synthesis and the canonical verdict
• assigns persistent Conclave-owned answer IDs that survive protocol phases, serialization, cache replay, synthesis, and verdict extraction
• separates protocol completed from ready, not_ready, and indeterminate decision readiness
• records secret-scanned receipts for every buffered Elite call, including synthesis, verdict extraction, and repair
• makes cache identity version-aware and threads one resolved custom-provider configuration through every call
• exposes async, sync, CLI, JSON, cache, and failure-exit behavior
• aligns README, PDD, architecture, documentation index, changelog, roadmap, and implementation plans

Why

Elite is an intentionally falsifiable attempt to improve consequential decision quality. The current guarantee is execution traceability and within-run answer provenance—not external source grounding, factual truth, or proof that consensus is correct.

Behavior

• each member phase requires three successful responders; larger councils may tolerate failures while three remain
• a failed member gate stops later work and returns not_ready with phase artifacts
• completed member phases remain distinct from decision readiness
• synthesis or required extraction failure is not_ready; disabled or inapplicable adjudication is indeterminate
• only a completed, synthesized run with a valid verdict is ready
• answer IDs trace model outputs inside a run; they are not external citations
• buffered receipts cover initial, critique, revision, synthesis, extraction, and repair attempts
• unknown cost remains None; latency and reported usage are aggregated from the complete receipt ledger
• Elite streaming is intentionally unsupported

Validation

• 561 tests passed locally
• GitHub Actions passed on Python 3.11, 3.12, and 3.13
• Ruff lint and format checks passed
• pip-audit passed
• Gitleaks passed; local Gitleaks scanned 89 commits with no leaks
• git diff --check origin/main...HEAD passed

Tracking

• Linear epic: DSE-690
• Horizon 0 acceptance items are complete
• Horizons 1–4 remain open and are governed by the decision-quality roadmap

Release boundary

This PR does not bump the package version, create a tag, publish a GitHub Release, or publish to PyPI.