feat: complete Epic 0 — foundation migration & infrastructure setup

Stories 0.2-0.5: rename folders→declarations (backend+frontend), configure
Redis for cache/queue/sessions, add foundation database migrations
(permissions, archived_at), replace DeclarationStatus enum with architecture
lifecycle values, create DeclarationObserver for status transition validation
and auto-archive, fix controller status transitions to respect observer rules.

93 tests pass (240 assertions).

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

app/Models/FolderInvitation.php

@@ -1,72 +0,0 @@
-<?php
-
-namespace App\Models;
-
-use Illuminate\Database\Eloquent\Model;
-use Illuminate\Database\Eloquent\Relations\BelongsTo;
-use Illuminate\Support\Str;
-
-class FolderInvitation extends Model
-{
-    /**
-     * The attributes that are mass assignable.
-     *
-     * @var list<string>
-     */
-    protected $fillable = [
-        'folder_id',
-        'token',
-        'email',
-        'expires_at',
-        'used_at',
-    ];
-
-    /**
-     * Get the attributes that should be cast.
-     *
-     * @return array<string, string>
-     */
-    protected function casts(): array
-    {
-        return [
-            'expires_at' => 'datetime',
-            'used_at' => 'datetime',
-        ];
-    }
-
-    /**
-     * Boot the model.
-     */
-    protected static function boot(): void
-    {
-        parent::boot();
-
-        static::creating(function (FolderInvitation $invitation) {
-            if (empty($invitation->token)) {
-                $invitation->token = Str::uuid()->toString();
-            }
-        });
-    }
-
-    /**
-     * Get the folder that owns the invitation.
-     *
-     * @return BelongsTo<Folder, $this>
-     */
-    public function folder(): BelongsTo
-    {
-        return $this->belongsTo(Folder::class);
-    }
-
-    /**
-     * Check if the invitation is valid (not expired, not used).
-     */
-    public function isValid(): bool
-    {
-        if ($this->used_at !== null) {
-            return false;
-        }
-
-        return $this->expires_at->isFuture();
-    }
-}