Change auto-lock default to at least 5 minutes to avoid user confusion when a transaction is in progress

**Describe the usability problem**
When a user connects to MetaMask wallet through an app and signs to authenticate their ownership of the wallet, it takes them more than a minute to decide to make a transaction (for example purchase of a coin, etc.). During this period, when MetaMask auto-locks itself (in 30 seconds by default), the connection between MetaMask and the app can break, the user may get network error or the user may have to reconnect and sign the wallet again. This confuses the user. Generally, apps can ask the user to set their auto-lock to 5 minutes, however most of the users cannot change their auto-lock preference and they are confused when they have to re-connect and sign again. This causes usability issues. Suggest changing default auto-lock to 5 minutes at least to enhance usability. This will be a nice compromise between security and usability.

**Expected behavior**
MetaMask should not auto-lock within 30 seconds. This is not enough time for anyone to do a transaction after connecting and signing their wallet. Auto-lock should be 5 minutes at the minimum. A tiny fix like this will enhance usability.

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**User impact | Usage frequency | Feasibility scores**
_How important is this to the user, what the user wants to accomplish | Daily, weekly, monthly | Small, medium, large_

Start by locating the mobile auto-lock setting and its current 30-second default in the TypeScript/React Native code. Confirm where the default is applied, then verify that a fresh installation keeps the wallet unlocked for at least five minutes instead of 30 seconds.

Written by the indexing model from the issue text.