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/Message.php

@@ -15,7 +15,7 @@ class Message extends Model
      * @var list<string>
      */
     protected $fillable = [
-        'folder_id',
+        'declaration_id',
         'type',
         'body',
         'sent_by_type',
@@ -38,13 +38,13 @@ class Message extends Model
     }
 
     /**
-     * Get the folder that owns the message.
+     * Get the declaration that owns the message.
      *
-     * @return BelongsTo<Folder, $this>
+     * @return BelongsTo<Declaration, $this>
      */
-    public function folder(): BelongsTo
+    public function declaration(): BelongsTo
     {
-        return $this->belongsTo(Folder::class);
+        return $this->belongsTo(Declaration::class);
     }
 
     /**