feat: add professional discrepancy center

[siracusa5]

Summary

Evolves the existing conflict workflow into a professional Discrepancy Center for structural alignment across ContextCake sources. It adds decision-ready evidence, transactional and recoverable resolutions, and governed rule learning while preserving the resolver contract and keeping semantic contradiction detection explicitly out of scope.

Changes

• detect section-content, authored-frontmatter, broken-link, and changed-after-decision discrepancies with stable revisions and coverage state
• add schema-v2 append-only decisions, guarded multi-file transactions, rollback, startup recovery, acknowledgements, reconciliation, legacy compatibility, and MCP disposition metadata
• suggest structural rules only after three consistent distinct decisions; require separate automation enablement and preserve recommendation-only team promotion
• replace the Conflicts surface with a filterable, keyboard-operable Discrepancy Center with N-way evidence, accurate added/removed diffs, complete history, and explicit demo simulation
• align API docs, product documentation, demo copy, and marketing language with the structural-discrepancy boundary
• prepare the coordinated Mac app and Web Demo release as version 0.6.0

Adversarial review fixes

• serialize failed automatic-attempt records with decisions so a blocked attempt cannot appear after a successful manual decision
• prevent API callers from spoofing rule authority or labeling manual decisions automatic
• revalidate the rule, ambiguity state, revision, coverage, source health, and writability inside the manifest lock immediately before automation
• replace set-membership comparisons with bounded sequence diffs that show both removed and added prose or structured lines
• preserve the console responsiveness context split while rebasing onto the latest main

Test Plan

• npm test
• console npm run typecheck
• console npm test -- --run — 318 tests
• console demo and live production builds
• site production build
• desktop tests — 103 tests
• packaged Mac app build and self-terminating smoke test
• npm run demo:verify
• fault-injected transaction replacement and recovery tests
• targeted rule-authority and two-way diff regressions
• light/dark browser checks at 760×560, 900×640, 1360×860, and 1600×1000
• CI checks pass

Notes

• Structural discrepancies never depend on an LLM or network service. Semantic entity matching and model-inferred contradictions remain future work.
• The legacy /api/conflict-resolutions route and existing conflicts[] fields remain compatible.
• Automatic actions require an explicitly approved per-rule automatic mode, settled healthy sources, a current revision, and one unambiguous action.
• The Web Demo never writes files or runs automatic rules.