docs: document friction reporting operations

[aaight]

Summary

Documents the finalized friction reporting behavior for operators and provider contributors.

Trello card: https://trello.com/c/69ff6af3bc5c526cc5faa2d4

Changes

• Documented the optional Friction PM slot across architecture/operator docs: Trello lists.friction, JIRA/Linear statuses.friction.
• Added ReportFriction / cascade-tools pm report-friction usage, including --details-file -, to gadget documentation.
• Explained that friction report materialization uses existing provider createWorkItem plus optional moveWorkItem, with no new adapter method or DB-backed friction index.
• Documented sidecar/outbox retry behavior, missing-slot handling, and non-blocking backend drain failures.
• Added a documentation regression test that pins the key operator/provider contract terms.

Verification

• npx vitest run --project unit-core tests/unit/architecture-docs.test.ts tests/unit/friction/format.test.ts tests/unit/friction/sidecar.test.ts tests/unit/friction/materialize.test.ts
• npx vitest run --project unit-backends tests/unit/backends/sidecarManager.test.ts tests/unit/backends/adapter.test.ts
• npm run lint:fix
• npm run lint
• npm run typecheck
• npm test

🕵️ codex · gpt-5.5 · run details

[nhopeatall]

LGTM - the documentation matches the implemented friction reporting contract, AGENTS.md is synchronized via the CLAUDE.md symlink, and the targeted architecture docs regression test passes locally.

🕵️ codex · gpt-5.5 · run details