feat(router): adopt portfolio routing for Auto

[KillerQueen-Z]

Summary

• replace Franklin's legacy Auto model selection with the shared deterministic portfolio router
• consume the product-neutral @blockrun/router-core package directly, with no ClawRouter runtime dependency
• select one model per user turn and pin it across the agent's internal tool/model rounds
• forward hard request capabilities from both the Franklin agent loop and OpenAI-compatible proxy
• preserve ordered model fallbacks and legacy eco / premium model aliases
• treat tool_choice: none as a hard no-tool constraint

Product validation

• clean install from the immutable Router Core commit tarball succeeded
• Franklin local test suite: 646 / 646 passed
• Franklin Proxy product integration:
  • blockrun/auto routes through the shared portfolio before forwarding
  • tool_choice: none remains a hard no-tool constraint
• real Franklin CLI Auto end-to-end: 5 / 5 passed
  • normal response
  • Bash tool execution
  • Write to Read in one agent session
  • multi-turn session cost accumulation
  • startup and clean exit without a model call

Dependency / merge order

Router Core is now an independent repository rather than a ClawRouter subpath dependency. This PR pins the immutable, checksummed commit tarball at 6a790eb, including the latest retired-model fallback cleanup, so Franklin and ClawRouter can review and merge their product integrations independently. A future npm release of @blockrun/router-core can replace the commit URL with a semver range without changing Franklin's adapter.

No benchmark package, payment path, or benchmark runtime is coupled into Franklin.