Document traverse-starter integration path for App-References v0.5.0 pin

[enricopiovesan]

Summary

`traverse-framework/App-References` is pinned to Traverse v0.3.0. The `traverse-cli app validate` and `traverse-cli app register` CLI surface required for Phase 2 shipped in v0.5.0. This ticket tracks the Traverse-side documentation needed to support App-References updating its pin to v0.5.0.

Why

App-References Phase 2 (issues #24, #6) requires:

• `traverse-cli app validate --manifest --json` ✅ shipped v0.5.0
• `traverse-cli app register --manifest --workspace --json` ✅ shipped v0.5.0
• Runtime loading of registered app state ✅ shipped v0.5.0

The only gap is that `docs/traverse-runtime.md` in App-References references v0.3.0 setup. Traverse should confirm v0.5.0 is the minimum supported version for downstream app registration consumers.

Definition of Done

• `quickstart.md` (or equivalent) in Traverse documents v0.5.0 as the minimum version for downstream apps that use `traverse-cli app validate/register`
• The v0.5.0 `cargo run -p traverse-cli -- serve` startup sequence is confirmed to write `.traverse/server.json` with the same schema as v0.3.0 (backward-compatible discovery)
• Release notes confirm App-References consumers should pin to v0.5.0 minimum for Phase 2

Unblocks

• `traverse-framework/App-References` ticket to update pin from v0.3.0 → v0.5.0