fix(cli): validate metadata.gatewayName type in normalizeSession

[ericksoa]

Bug

In src/lib/onboard-session.ts, normalizeSession copies metadata.gatewayName without checking its type. A persisted payload like { "metadata": { "gatewayName": 123 } } survives normalization, so loadSession() can return a Session where metadata.gatewayName is not a string.

Fix

Add typeof gatewayName === "string" check before copying it into the normalized session.

Found by

CodeRabbit review on #1272. Pre-existing from original JS.

[latenighthackathon]

Our PR #1286 implements this fix — adds a typeof check in normalizeSession so non-string gatewayName values are dropped and the default "nemoclaw" is used instead. Includes a regression test for numeric gatewayName.