[Invoice-Liquidity-Network] Enforce semver-breaking-change detection on the SDK's public API surface

## Observed symptom Enforce semver-breaking-change detection on the SDK's public API surface The `sdk/` package has no automated guard against accidental breaking changes shipping in a minor/patch release — `packages/` consumers and the CLI currently discover breakage only after publish, which is unacceptable once external integrators depend on mainnet SDK stability. **Requirements and context** - Generate a public API snapshot for `sdk/` (extend `scripts/generate-types.ts` output or use a dedicated API-extractor) and commit it as the compatibility baseline - Add a CI check that diffs the current API surface against the baseline and fails the build when a breaking change isn't paired with a major version bump in the changeset - Cover at minimum: removed/renamed exports, changed function signatures, changed enum members, narrowed return types - Document the enforcement policy in `docs/sdk-api-reference.md` ## Environment GitHub Invoice-Liquidity-Network/Invoice-Liquidity-Network #1029 ## Trigger / context Public GitHub report in Invoice-Liquidity-Network/Invoice-Liquidity-Network (FRESH_14D). ## Source evidence - https://github.com/Invoice-Liquidity-Network/Invoice-Liquidity-Network/issues/1029 (2026-09-23T14:40:21Z) — evidence_class: PRIMARY_ISSUE_REPORT — #1029 ## Freshness - classification: FRESH_14D - retrieved_at: 2026-10-02T10:42:44.319212Z - scout_id: Cab20b67eee ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.