fix: ReferenceError context is not defined in streamResponse (#135)

streamResponse was referencing bare `context` for the IP-level rate-limit
circuit breaker, but `context` was never passed to the function. Now passes
`context` through the `deps` parameter and accesses it as `deps.context`,
matching the pattern used by other shared state (cachePolicy, tools, etc.).

Fixes: all Claude models crashing with "Handler error: ReferenceError:
context is not defined at chat.js:3223"