fix(router): handle Claude routing failures

[doedja]

Summary

• normalize Claude's terminal [1m] marker before Kenari model lookup and forwarding
• preserve native Claude model IDs unchanged
• terminate downstream responses when an upstream stream aborts or closes early
• add routing-matrix and interrupted-stream regression tests

Root cause

Claude Code can append [1m] to a configured role model. The router previously looked up the suffixed value literally, so kenari/minimax-m3[1m] failed even though minimax-m3 exists and supports a 1M context.

The response proxy also piped upstream data without handling response-side abort, error, or premature close events. A truncated upstream stream could leave Claude Code waiting until its five-minute stalled-response watchdog fired.

User impact

Claude Auto mode classifier requests can use 1M-capable Kenari role models. Interrupted parent or subagent streams fail immediately instead of remaining open for five minutes.

Validation

• npm test: 91 passed, 0 failed
• lowercase and uppercase [1m] markers
• malformed non-terminal marker rejection
• native model preservation
• interrupted SSE propagation