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

internal/sshclient/hostkey.go

@@ -7,7 +7,7 @@ import (
 	"net"
 	"time"
 
-	"github.com/andydixon/nexus/internal/models"
+	"github.com/andydixon/link/internal/models"
 	"golang.org/x/crypto/ssh"
 )
 

internal/sshclient/portforward.go

@@ -13,7 +13,7 @@ import (
 	"net"
 	"sync"
 
-	"github.com/andydixon/nexus/internal/models"
+	"github.com/andydixon/link/internal/models"
 	"golang.org/x/crypto/ssh"
 )
 

internal/sshclient/sshclient.go

@@ -13,8 +13,8 @@ import (
 	"sync"
 	"time"
 
-	"github.com/andydixon/nexus/internal/models"
-	"github.com/andydixon/nexus/internal/terminalenv"
+	"github.com/andydixon/link/internal/models"
+	"github.com/andydixon/link/internal/terminalenv"
 	"github.com/pquerna/otp/totp"
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/net/proxy"

internal/sshclient/sshclient_test.go

@@ -7,7 +7,7 @@ import (
 	"testing"
 	"time"
 
-	"github.com/andydixon/nexus/internal/models"
+	"github.com/andydixon/link/internal/models"
 	"golang.org/x/crypto/ssh"
 )