Rebrand: Nexus Terminal → Alchementary Link

Renames the product across the codebase: Go module path, config/data
paths, keychain service name, export file extension, build tooling,
docs, and UI text. Sidebar brand mark now reads ">_ AlchementaryLink"
with "Alchementary" in the connection-group gold accent colour, and
the window title is "Alchementary Link".

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019T8bJS8BCtY5GeSG2HBj1n

frontend/package-lock.json

@@ -1,11 +1,11 @@
 {
-  "name": "nexus-terminal-frontend",
+  "name": "alchementary-link-frontend",
   "version": "0.1.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
-      "name": "nexus-terminal-frontend",
+      "name": "alchementary-link-frontend",
       "version": "0.1.0",
       "hasInstallScript": true,
       "dependencies": {