refactor(v5): remove Project model and consolidate v5 migrations

Drop v5_projects table, Project model, and related alter-table
migrations; fold cluster_id and nullable private_key_id into the
initial v5_servers migration; rename migration files to v5_ prefix;
strip cooldServers/privateKeys/teams props from HomeController and
Home page.

app/Models/V5/Project.php

@@ -1,29 +0,0 @@
-<?php
-
-namespace App\Models\V5;
-
-use App\Models\Team;
-use App\Models\User;
-use Illuminate\Database\Eloquent\Relations\BelongsTo;
-
-class Project extends V5Model
-{
-    protected $table = 'v5_projects';
-
-    protected $fillable = [
-        'team_id',
-        'created_by_user_id',
-        'name',
-        'description',
-    ];
-
-    public function team(): BelongsTo
-    {
-        return $this->belongsTo(Team::class);
-    }
-
-    public function creator(): BelongsTo
-    {
-        return $this->belongsTo(User::class, 'created_by_user_id');
-    }
-}