Implement spec 057 manifest execution modes

[enricopiovesan]

Summary

Implements the first spec 057 slice for app bundle validation: component manifests now support explicit execution_mode values for wasm and compatible, and traverse-cli app validate reports execution-mode metadata without requiring compatible components to declare WASM artifacts.

Governing Spec

• 057-embeddable-runtime-host
• 044-application-bundle-manifest
• 004-spec-alignment-gate
• 028-schema-alignment-gate-v02
• 031-supply-chain-hardening
• 040-contractual-enforcement-gate

Project Item

• Closes Spec + SDK: embeddable in-app WASM runtime host for downstream platform clients #553
• Project 1 item: https://github.com/orgs/traverse-framework/projects/1/

What Changed

• Contracts changed: none.
• Runtime behavior changed: app manifest loading now defaults omitted component execution_mode to wasm, validates WASM and compatible component field requirements separately, and exposes optional WASM artifact metadata for compatible components.
• Compatibility impact: existing WASM manifests without execution_mode remain valid.
• ADR needed or linked: no ADR needed; this is governed by approved spec 057.

Validation

• Spec alignment checked: implemented spec 057 FR-014 and FR-020 through FR-024; scripts/ci/spec_alignment_check.sh requires a PR body file and is expected to run in CI against this body.
• Contract alignment checked: no contract schema changes.
• Tests updated and passing: cargo test -p traverse-registry --test application_manifest.
• Core coverage preserved: cargo test -p traverse-registry -p traverse-cli.
• Required validation gates passing:
  • bash scripts/ci/embedder_conformance/reference_cli.sh
  • bash scripts/ci/downstream_app_bundle_registration_smoke.sh
  • cargo clippy -p traverse-registry -p traverse-cli -- -D warnings

Notes

This PR adds scripts/ci/embedder_conformance/reference_cli.sh as the initial checked-in conformance entry point. Full platform embedder implementations remain downstream work for the reference-apps platform tickets.