IGL 1.1.0 — Merkle inclusion proofs + runtime attestation

Audit strengthening, informed by a comparative review of MCP security frameworks.

Added

• Merkle inclusion proofs on the journal (store.js): merkleRoot(),
  inclusionProof(seq), verifyInclusion() an auditor verifies a single
  disclosed entry against a published root without access to the rest of the
  chain. Privacy-preserving audit on top of the linear hash chain.
• Runtime attestation in receipts (sign.js): every trace and head
  receipt carries runtime, a SHA-256 digest of the runtime's own source
  manifest, inside the signed envelope. Which governed build produced a
  receipt is settled by re-computation, not confidence.
• Receipt envelope verification now authenticates every field, present or
  future — only key material and signature are stripped.

Compatibility

• Receipts signed by 1.0.0 (envelope without runtime) still verify.

Tests

• 124/124 npm ci && npm test from a clean clone reproduces everything.