fix(i18n): render translated label inside role SelectValue

Base UI's <SelectValue> with no children does not reliably extract
text from the selected <SelectItem> when the item's children is a
function call (e.g. tRoles(r.value)) — the trigger falls back to
displaying the raw enum string ('admin', 'agent', 'viewer').

Render the translated label explicitly as children of <SelectValue>
so the trigger always shows the human-readable role name.

Scope: only the two role selectors in Settings (matches this PR's
theme). The same pattern affects ~5 other sites (template-manager
header format, button type; ai-config provider and handoff target;
flows/broadcasts) — those are left as follow-up and tracked in #375.

Part of #375

src/components/settings/invite-member-dialog.tsx

@@ -274,7 +274,7 @@ export function InviteMemberDialog({
                   onValueChange={(v) => v && setRole(v as InviteRole)}
                 >
                   <SelectTrigger className="w-full bg-muted border-border text-foreground">
-                    <SelectValue />
+                    <SelectValue>{tRoles(role)}</SelectValue>
                   </SelectTrigger>
                   <SelectContent>
                     <SelectItem value="admin">{tRoles('admin')}</SelectItem>

src/components/settings/members-tab.tsx

@@ -428,7 +428,7 @@ export function MembersTab() {
                           className="w-32 bg-muted border-border text-foreground"
                           disabled={isBusy}
                         >
-                          <SelectValue />
+                          <SelectValue>{tRoles(member.role)}</SelectValue>
                         </SelectTrigger>
                         <SelectContent>
                           {EDITABLE_ROLES.map((r) => (