fix task 29: expose username and email as separate fields on entry detail - VaultEntry already had both as distinct optional fields (username, email), but EntryDetailScreen only ever rendered whichever was present and silently dropped the row entirely for a blank one, with no way to add the missing field from the detail screen at all - a real gap vs. the browser, which shows a '+ add username'/'+ add email' link for the missing field. Added per-field show/hide state seeded from whether the entry already has a value, with '+ add username'/'+ add email' links (reusing the existing '+ add another url' link pattern) that reveal an EditableFieldRow with the matching placeholder when tapped. Live-verified on the GitHub demo entry (username only): '+ add email' link appears, tapping it reveals an EMAIL row with 'add email' placeholder ready to edit.

@@ -254,23 +254,54 @@254254                             placeholder = "add url",255255                         )256256                     }257-                    e.username?.takeIf { it.isNotBlank() }?.let { v ->257+                    // Browser distinguishes USERNAME and EMAIL as separate258+                    // optional fields, with a "+ add X" link for whichever the259+                    // entry doesn't have yet — an entry can carry both. This260+                    // used to just omit the row entirely for a blank field,261+                    // with no way to add it from the detail screen.262+                    var showUsernameField by remember(e.id) { mutableStateOf(!e.username.isNullOrBlank()) }263+                    var showEmailField by remember(e.id) { mutableStateOf(!e.email.isNullOrBlank()) }264+                    if (showUsernameField) {258265                         EditableFieldRow(259-                            label = "username", field = "username", value = v,266+                            label = "username", field = "username", value = e.username.orEmpty(),260267                             copied = copiedField == "username",261-                            onCopy = { vm.copy("username", v) },268+                            onCopy = { vm.copy("username", e.username) },262269                             onSave = { vm.updateField("username", it) },263270                             suggestions = identitySuggestions,271+                            placeholder = "add username",264272                         )265273                     }266-                    e.email?.takeIf { it.isNotBlank() }?.let { v ->274+                    if (showEmailField) {267275                         EditableFieldRow(268-                            label = "email", field = "email", value = v,276+                            label = "email", field = "email", value = e.email.orEmpty(),269277                             copied = copiedField == "email",270-                            onCopy = { vm.copy("email", v) },278+                            onCopy = { vm.copy("email", e.email) },271279                             onSave = { vm.updateField("email", it) },272280                             suggestions = identitySuggestions,281+                            placeholder = "add email",273282                         )283+                    }284+                    if (!showUsernameField || !showEmailField) {285+                        Row(horizontalArrangement = Arrangement.spacedBy(16.dp)) {286+                            if (!showUsernameField) {287+                                Text(288+                                    "+ add username", color = accent, style = PeachType.labelMono,289+                                    modifier = Modifier290+                                        .clip(RoundedCornerShape(6.dp))291+                                        .clickable { showUsernameField = true }292+                                        .padding(vertical = 6.dp),293+                                )294+                            }295+                            if (!showEmailField) {296+                                Text(297+                                    "+ add email", color = accent, style = PeachType.labelMono,298+                                    modifier = Modifier299+                                        .clip(RoundedCornerShape(6.dp))300+                                        .clickable { showEmailField = true }301+                                        .padding(vertical = 6.dp),302+                                )303+                            }304+                        }274305                     }275306                     AdditionalUrlRows(276307                         urls = e.additionalUrls.orEmpty(),