v0.17.0

Added

• Task-class routing (routing module): classify is an LLM-free, deterministic
  policy that sorts a prompt into rule, slm, or heavy by its length and a
  small keyword set, and TieredChatClient is a chat backend that dispatches
  each request to the backend for its class (falling back to a default), so
  trivial requests are answered cheaply and only hard ones reach a heavy model.
• The model worker gains a tiered provider (a rule path plus SLM and heavy HTTP
  models) and a --heavy-model option. classify, TaskClass, and
  TieredChatClient are exported.
• A committed routing benchmark (benchmarks/routing_benchmark.py): a fixed
  prompt set with checked-in results reporting the class distribution, the
  per-prompt decision, and a verification that a tiered client dispatches each
  prompt to its class. Decisions are exact and reproducible; backend latency is
  out of the offline scope (the slm/heavy tiers need a live model server).