fix(compliance): release 3.0.16 storyboard fixes

[bokelley]

Summary

Release 3.0.16 on the 3.0.x line with compliance storyboard fixes for the runner failures reported against the stable bundle.

This backports the fixed storyboard source for:

• universal idempotency webhook placeholder behavior
• universal schema-validation past-start rejection
• universal security initialized-session/static credential probes
• universal webhook-emission runner webhook URL requirements
• media-buy state-machine setup before pause/resume/cancel transitions

3.0.15 already exists as released artifacts and a remote tag, so this ships the next patch release instead of mutating 3.0.15.

Validation

• npm run build:compliance -- --release
• npm run build:protocol-tarball -- --release
• npm run sign:protocol-tarball (skipped locally; SIGN_PROTOCOL_TARBALL=true not set)
• npm run test:schemas
• npm run test:storyboard-sample-request-schema
• npm run test:storyboard-response-schema
• npm run test:storyboard-context-entity
• npm run test:storyboard-contradictions
• npm run test:storyboard-test-kits
• git diff --check && git diff --cached --check
• pre-commit hook: npm run test:unit && npm run test:test-dynamic-imports && npm run typecheck

Notes

No existing dist/compliance/3.0.15, dist/schemas/3.0.15, or dist/protocol/3.0.15.* files are modified. The release adds new 3.0.16 artifacts.

[bokelley]

Closing in favor of #5533, which uses the changeset-release/ branch prefix expected by the consumed-changeset release workflow.