Agent-mode classifies client-side decode errors as connection_error

## Bug

When a server response fails to decode (schema drift), the agent-mode structured error reports `"error_type": "connection_error"` with hints like "Check network connectivity" — misleading, since the HTTP request actually succeeded and the network is fine. It's a client-side deserialization failure.

## Root cause (Speakeasy)

The generated `classifyErrorType(statusCode)` maps `statusCode == 0` → `connection_error`. A client-side JSON decode error carries no HTTP status (0), so it's lumped in with genuine connection failures.

## Stopgap fix (retire when upstream is fixed)

`.speakeasy/patches/internal/output/agentmode.go.patch`: `classifyErrorType` now also takes the error; when `statusCode == 0` and the error is (or wraps) a `*json.UnmarshalTypeError` / `*json.SyntaxError`, it returns `response_error` with an actionable hint ("the response didn't match the expected schema; retry with `-o json`").

**To retire:** once the generated agent-mode classifier distinguishes response-decode/parse errors from connection errors, drop that hunk.

## Refs

- Introduced by #23
- Related: the `settings get` / `updateSchedule.hours` decode bug is the trigger that surfaced this.
- Upstream: file to speakeasy-api/speakeasy (generated agent-mode error classification).

Start with .speakeasy/patches/internal/output/agentmode.go.patch and inspect the generated classifyErrorType implementation it changes. Reproduce the settings get or updateSchedule.hours decode failure if possible, then verify that schema and JSON parse errors are reported as response_error with the actionable hint rather than connection_error; retire the hunk if the upstream classifier already handles this.

Written by the indexing model from the issue text.