Add app state machine manifest validation

[enricopiovesan]

Governing Spec

• 052-app-state-machine
• 044-application-bundle-manifest

Project Item

• Closes Spec + runtime: app-level state machine definition in app manifest #525

Validation

• python3 -m json.tool specs/governance/approved-specs.json
• cargo test -p traverse-cli app_validate -- --nocapture
• bash scripts/ci/rust_checks.sh
• bash scripts/ci/repository_checks.sh
• git diff --check

Notes

• Implements the manifest schema and validation slice. Runtime command dispatch, state subscriptions, session listing, and conditional output-based transitions remain in the follow-up Project tickets already tracking those surfaces.