feat(servers/settings): magic string invites, Navidrome admin share, and add-user validation (#258)

* feat(servers): magic string invites and duplicate-aware labels

Add psysonic1- share payloads (URL, Subsonic credentials, optional server
name). Login and add-server forms decode on input and keep magic field
below standard fields. Navidrome User Management generates strings after
PUT password updates where required. Resolve duplicate display names as
username@host in chrome, settings, and login.

* feat(servers): tighten magic-string import and admin share flow

After a decoded magic string, username is read-only and the password field
shows a fixed-length mask so length is not inferred. Password reveal stays
disabled until saved-server quick connect (login) or reopening the add-
server form. Navidrome admin share UI persists the password via API before
copy and adds a plaintext-handling disclaimer. Locales updated.

* feat(settings): save new Navidrome user and copy magic string

Add a non-admin "Save and get magic string" flow: create the user, assign
libraries when needed, then encode credentials to the clipboard. Reuse
the plaintext-handling disclaimer without the password-update hint meant
for edits. Strings added for all locales.

* fix(settings): tighten Navidrome add-user validation and submit feedback

Require username, display name, and a non-empty password (trimmed) for new
users; gate Save and “save and get magic string” on explicit checks with
toast feedback. Show red borders only after a failed submit, and clear
them when the user fills the fields. When editing, keep an empty password
as “unchanged” and validate identity fields with a dedicated message.
Strings: userMgmtValidationMissingIdentity across locales.

src/locales/en.ts

@@ -352,6 +352,9 @@ export const enTranslation = {
     urlRequired: 'Please enter a server URL.',
     savedServers: 'Saved Servers',
     addNew: 'Or add a new server',
+    orMagicString: 'Or magic string',
+    magicStringPlaceholder: 'Paste a share string (psysonic1-…)',
+    magicStringInvalid: 'Invalid or unreadable magic string.',
   },
   connection: {
     connected: 'Connected',
@@ -511,6 +514,19 @@ export const enTranslation = {
     userMgmtUpdated: 'User updated.',
     userMgmtDeleted: 'User deleted.',
     userMgmtValidationMissing: 'Username, display name and password are required.',
+    userMgmtValidationMissingIdentity: 'Username and display name are required.',
+    userMgmtMagicStringGenerate: 'Generate magic string',
+    userMgmtSaveAndMagicString: 'Save and get magic string',
+    userMgmtMagicStringPasswordNavHint:
+      'Navidrome will save this password for the user. If it differs from the current one, the server will update the login password.',
+    userMgmtMagicStringPlaintextWarning:
+      'Share the magic string carefully: it contains an unencrypted password (encoding is not encryption). Anyone with the full string can sign in as this user.',
+    userMgmtMagicStringCopied: 'Magic string copied to clipboard.',
+    userMgmtMagicStringCopyFailed: 'Could not copy to clipboard.',
+    userMgmtMagicStringLoginFailed: 'Password check failed — credentials could not be verified.',
+    userMgmtMagicStringModalTitle: 'Generate magic string',
+    userMgmtMagicStringModalDesc: 'Enter the Subsonic password for "{{username}}". It is included in the copied magic string.',
+    userMgmtMagicStringModalConfirm: 'Copy string',
     audiomuseTitle: 'AudioMuse-AI (Navidrome)',
     audiomuseDesc:
       'Turn on if this server has the <pluginLink>AudioMuse-AI Navidrome plugin</pluginLink> configured. Enables Instant Mix from tracks and uses server-side similar artists instead of Last.fm on artist pages.',