feat(drift): add content drift reports

[bntvllnt]

Summary

• Add CH-P2-04 drift CLI command and detect_content_drift MCP tool in report-only mode.
• Detect name, scope, mixed-responsibility, hidden-side-effect, shape, orphan-scope, and misplaced-test drift with deterministic IDs/evidence.
• Wire operation registry, text formatter, MCP hints, real-codebase dogfood, docs, llms files, and roadmap status.
• Split drift internals into clear seams: types, tokens, evidence, profiles, findings, and thin public index.

Validation

• code-review: CLEAN (/tmp/code-review-content-drift.json)
• pnpm typecheck
• pnpm lint
• pnpm build
• pnpm vitest run tests/drift.e2e.test.ts tests/operation-registry.test.ts tests/operation-registry.e2e.test.ts tests/mcp-tools.test.ts --reporter=verbose --pool threads --no-file-parallelism --maxWorkers=1 — 72 tests
• pnpm test — 35 files / 472 tests
• pnpm verify:cli-real — 68/68 checks
• git diff --check
• dogfood: node dist/cli.js drift . --scope src/drift --min-score 35 --json --force — 0 findings

Release

• Canary train only after merge.
• No stable release in this PR.