Pin Traverse runtime to v0.3.0 and document local discovery

[enricopiovesan]

Summary

Pins the Traverse runtime dependency to v0.3.0 and documents the complete local setup sequence, resolving open questions 1–3 from the plan. All apps in this repo target this baseline.

Definition of Done

• docs/traverse-runtime.md — canonical setup reference: version, start command, discovery file, API surface table, browser config, Phase 2 CLI commands, CI env var overrides
• CLAUDE.md — Traverse Runtime section with version, address, and start commands
• AGENTS.md — Traverse Runtime section with discovery snippet and TRAVERSE_REPO override
• scripts/ci/repository_checks.sh — requires docs/traverse-runtime.md
• scripts/ci/phase1_smoke.sh — already updated to use .traverse/server.json discovery

Validation

bash scripts/ci/repository_checks.sh
# PASS: all required files present

# Local runtime verification
git clone https://github.com/traverse-framework/Traverse.git /tmp/traverse
cd /tmp/traverse && git checkout v0.3.0
cargo run -p traverse-cli -- serve &
curl -s http://127.0.0.1:8787/healthz | jq .
# {"status":"ok","api_version":"v1","workspace_default":"local-default",...}

Architecture boundary

Docs only — no business logic, no Traverse internals imported. Runtime version is an external pinned dependency.

Closes #9