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/Http/Controllers/FolderMentionController.php

@@ -1,59 +0,0 @@
-<?php
-
-namespace App\Http\Controllers;
-
-use App\Http\Requests\StoreFolderMentionRequest;
-use App\Models\Folder;
-use App\Models\User;
-use App\Models\Workspace;
-use App\Notifications\FolderMentionNotification;
-use Illuminate\Http\RedirectResponse;
-use Illuminate\Http\Request;
-use Illuminate\Support\Facades\Cache;
-
-class FolderMentionController extends Controller
-{
-    protected function currentWorkspace(Request $request): Workspace
-    {
-        $workspaceId = $request->session()->get('current_workspace_id');
-
-        return Workspace::query()->findOrFail($workspaceId);
-    }
-
-    protected function authorizeFolder(Workspace $workspace, Folder $folder): void
-    {
-        if ($folder->workspace_id !== $workspace->id) {
-            abort(404);
-        }
-    }
-
-    public function store(StoreFolderMentionRequest $request, Folder $folder): RedirectResponse
-    {
-        $workspace = $this->currentWorkspace($request);
-        $this->authorizeFolder($workspace, $folder);
-
-        $userRole = $workspace->users()
-            ->where('users.id', $request->user()->id)
-            ->first()
-            ?->pivot
-            ?->role
-            ?->value;
-
-        if (! in_array($userRole, ['owner', 'manager'])) {
-            abort(403);
-        }
-
-        $validated = $request->validated();
-        $targetUser = User::findOrFail($validated['user_id']);
-
-        $targetUser->notify(new FolderMentionNotification(
-            $folder,
-            $request->user(),
-            $validated['message'],
-        ));
-
-        Cache::forget("user:{$targetUser->id}:unread_notifications");
-
-        return back()->with('flash', ['type' => 'success', 'message' => 'Notification envoyée.']);
-    }
-}