feat: implement Phase 6 — Software Deployment

Backend:
- SoftwarePackage model (Name, Version, OsType, PackageManager, PackageName, InstallerUrl, Checksum, SilentArgs)
- RmmDbContext: SoftwarePackages DbSet + unique index on (Name, Version, OsType)
- SoftwarePackagesController: full CRUD with OsType filter
- DeployController: POST /api/v1/deploy creates InstallSoftware/UninstallSoftware TaskItem
- EF Migration: AddSoftwarePackages (20260319130448)

Go Agent:
- internal/deployer/deployer.go: Install() and Uninstall() with:
  - Chocolatey (Windows), apt/dnf (Linux), auto-detect
  - Direct installer fallback: HTTP download + SHA256 verify + silent install
  - Supports .msi, .exe (Windows) and .deb, .rpm (Linux)
- main.go: COMMAND_TYPE_INSTALL_SOFTWARE and COMMAND_TYPE_UNINSTALL_SOFTWARE routed to deployer

Frontend:
- SoftwarePage: Katalog tab (CRUD, OS filter, smart package manager select) + Deploy tab
- api/types.ts: SoftwarePackage, PackageManager, DeployRequest/Response types
- api/client.ts: softwarePackagesApi and deployApi
- App.tsx: Software nav item with Package icon

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Agent/cmd/agent/main.go

@@ -13,6 +13,7 @@ import (
 	"nexusrmm.local/agent/internal/collector"
 	"nexusrmm.local/agent/internal/config"
 	"nexusrmm.local/agent/internal/connection"
+	"nexusrmm.local/agent/internal/deployer"
 	"nexusrmm.local/agent/internal/executor"
 	pb "nexusrmm.local/agent/pkg/proto"
 )
@@ -128,6 +129,10 @@ func executeCommand(ctx context.Context, client *connection.GrpcClient, agentID
 	switch cmd.Type {
 	case pb.CommandType_COMMAND_TYPE_SHELL:
 		result = executor.Execute(ctx, cmd.Payload, 300)
+	case pb.CommandType_COMMAND_TYPE_INSTALL_SOFTWARE:
+		result = deployer.Install(ctx, cmd.Payload)
+	case pb.CommandType_COMMAND_TYPE_UNINSTALL_SOFTWARE:
+		result = deployer.Uninstall(ctx, cmd.Payload)
 	default:
 		result = &executor.Result{ExitCode: -1, Stderr: fmt.Sprintf("unknown command type: %v", cmd.Type)}
 	}