Release v0.3.5 native Pi and OpenCode routing

[regenrek]

Summary

• make Pi Subagents the only Pi workflow and keep the active Pi session as orchestrator
• add native provider-qualified routing for Pi and OpenCode
• remove isolated Pi workers and the non-functional Codex Gateway path
• refresh current model selectors, generated catalog, bundles, and v0.3.5 release notes

Verification

• cargo test --lib — 52 passed
• focused website Vitest suites — 68 passed
• cargo run --quiet -p xtask -- release verify --inventory-only — passed
• cargo fmt --all -- --check — passed
• git diff --check — passed
• Planr native-routing and Codex hard-cut audits — hold

Secret and package checks were intentionally left to CI.