[3/3] app-server: configure environment connection timeout

[sayan-oai]

Why

Remote environments registered through environment/add currently use the fixed 10-second WebSocket connection timeout. Slow-starting executors need a caller-selected connection window, but this should not add retry policy or couple exec-server behavior to Core’s deferred_executor feature.

Make the timeout an optional part of the existing experimental request. Existing clients continue using the current default, while callers that know an executor may take longer can request a larger window explicitly.

Depends on #28683.

What changed

• Add optional connectTimeoutMs to EnvironmentAddParams and document it in the app-server README.
• Pass the optional timeout through EnvironmentRequestProcessor into one EnvironmentManager::upsert_environment() path; the manager applies the existing default when it is omitted.
• Preserve the existing single-attempt lifecycle. The configured value controls WebSocket connection and handshake time for both initial connection and later reconnects; initialization retains its separate timeout.
• Add an app-server integration test that sends the real JSON-RPC request and verifies a stalled handshake observes the requested timeout.

Test plan

• just test -p codex-app-server-protocol
• just test -p codex-exec-server
• just test -p codex-app-server environment_add_applies_connect_timeout

Rollout

This is additive and does not enable deferred_executor. Callers should send a non-default timeout only after a compatible app-server is deployed; omitted or null values retain the existing 10-second default.

[pakrym-oai]

delete the proxy method

[pakrym-oai]

if you need fallback make the parameter optional