[Feature Request] Seamless KDE Wallet auto-unlock when user has a password set in Desktop Mode

Your system information

• Steam client version: 1785799196
• SteamOS version: 3.8.16
• Opted into Steam client beta?: No
• Opted into SteamOS beta?: No
• Have you checked for updates in Settings > System?: Yes

Please describe your issue in as much detail as possible:

When using browsers like Brave or Chrome in Desktop Mode on SteamOS, users are prompted to enter their deck password to unlock KDE Wallet upon the first browser launch after booting into the session.
Since SteamOS uses autologin for the deck account, the PAM module cannot automatically pass the user's password to KDE Wallet upon system boot, leaving the wallet locked even if the account password matches the wallet password.

It would be great if SteamOS could handle KDEWallet / system keyring unlocking automatically during Desktop Mode session initialization (e.g., via TPM integration, customized SDDM/PAM config, or a built-in SteamOS helper). This way, users with password-protected accounts wouldn't have to manually type their password into the KDE Wallet prompt every time they start a new session and open their browser for the first time.

This would greatly improve Desktop Mode UX for users who use browsers for daily tasks while keeping their session encrypted and secure.

Steps for reproducing this issue:

1. Set a password for the deck user account and ensure KDE Wallet is enabled, using the exact same password.
2. Boot the Steam Machine directly into Desktop Mode (or switch to Desktop Mode from Gaming Mode).
3. Launch a Chromium-based browser (e.g., Brave or Google Chrome) for the first time during this session.
4. Notice the KDE Wallet Service popup asking for a password to unlock 'kdewallet', instead of it being unlocked automatically in the background.

Start by tracing Desktop Mode session initialization, including the SDDM/PAM configuration and KDE Wallet unlock flow mentioned in the report. Compare possible TPM, PAM, or SteamOS helper approaches, then verify that a matching account and wallet password unlocks the wallet without a browser prompt while preserving the stated security expectations.