[client] Send the login hint from the desktop UI's session extend

RequestExtend left the hint empty and relied on the daemon's
GetLoginHint fallback. That fallback reads the per-profile state file
from the calling process's user config dir, so the root-owned daemon
looks under /root/.config/netbird and never finds the file the UI wrote
under the user's own config dir. Every session extend therefore went out
without a login_hint, leaving the IdP to guess the account.

Resolve it in the UI instead, which runs as the logged-in user and
already reads the same file for Profiles.List. Mirrors what the CLI's
extend path does.

client/internal/profilemanager/profilemanager.go

@@ -165,6 +165,11 @@ func (pm *ProfileManager) setActiveProfileState(id ID) error {
 }
 
 // GetLoginHint retrieves the email from the active profile to use as login_hint.
+//
+// TODO: only works when called as the logged-in user; the root-owned daemon
+// resolves the state file under /root/.config/netbird and always gets "".
+// Every caller now fills the hint itself, so dropping this and the daemon-side
+// fallbacks in client/server/server.go is the suggested fix.
 func GetLoginHint() string {
 	pm := NewProfileManager()
 	activeProf, err := pm.GetActiveProfile()