refactor: drop the Alchementary Link data migration

Startup no longer looks for an AlchementaryLink data directory to copy
into NexusTerminal, and the 'Imported your Alchementary Link data' toast
and the migration docs are gone. Existing Alchementary Link installs are
no longer picked up automatically.

docs/user-manual.md

@@ -16,7 +16,7 @@
 12. Security and credentials
 13. Import and export
 14. Settings and updates
-15. Data locations and migration from Alchementary Link
+15. Data locations
 16. Troubleshooting
 
 ---
@@ -404,7 +404,7 @@ Nexus Terminal checks for a new version once at launch. When one is available, t
 
 ---
 
-## 15. Data locations and migration from Alchementary Link
+## 15. Data locations
 
 ### Data locations
 
@@ -424,15 +424,6 @@ The directory holds:
 
 Credentials saved in the OS keychain are stored under the service name `NexusTerminal`.
 
-### Migrating from Alchementary Link
-
-On first run, if Nexus Terminal has no database yet and an Alchementary Link data directory (`AlchementaryLink`, in the same parent folder) exists, Nexus Terminal **copies** `link.db` to `nexus.db`, along with the `vault/` and `recordings/` directories, and shows a toast saying where the data came from. The Alchementary Link directory is left untouched.
-
-- If a `NexusTerminal/nexus.db` already exists (for example from a version before the Alchementary Link rebrand), it is used as-is and nothing is copied.
-- Keychain entries saved under `AlchementaryLink` are found the first time they are needed and copied to `NexusTerminal`. The old entries are not deleted.
-- Your vault master password is unchanged.
-- Trigger rules and SFTP bookmarks from Alchementary Link are not migrated; recreate them in Nexus Terminal.
-
 ---
 
 ## 16. Troubleshooting