docs: consolidate documentation into organized structure

- Move 12 markdown files from root to docs/ subdirectories
- Organize documentation by category:
  • docs/troubleshooting/ (1 file)  - Technical troubleshooting guides
  • docs/deployment/      (4 files) - Deployment and security documentation
  • docs/guides/          (3 files) - Feature-specific guides
  • docs/planning/        (4 files) - Planning and improvement proposals

Root directory cleanup:
- Reduced from 16 to 4 markdown files in root
- Only essential project files remain:
  • CLAUDE.md (AI instructions)
  • README.md (Main project readme)
  • CLEANUP_PLAN.md (Current cleanup plan)
  • SRC_STRUCTURE_IMPROVEMENTS.md (Structure improvements)

This improves:
✅ Documentation discoverability
✅ Logical organization by purpose
✅ Clean root directory
✅ Better maintainability

src/Application/Campaign/ShowCampaign.php

@@ -0,0 +1,84 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Application\Campaign;
+
+use App\Framework\Attributes\Route;
+use App\Framework\Http\Method;
+use App\Framework\Router\Result\ViewResult;
+use App\Framework\Http\Session\Session;
+use App\Framework\Meta\MetaData;
+
+/**
+ * Show Campaign Landing Page
+ *
+ * Displays public campaign landing page with pre-save functionality
+ */
+final readonly class ShowCampaign
+{
+    public function __construct(
+        private CampaignService $campaignService
+    ) {}
+
+    #[Route(path: '/campaign/{slug}', method: Method::GET)]
+    public function __invoke(string $slug, Session $session): ViewResult
+    {
+        // Fetch campaign data
+        $campaign = $this->campaignService->findBySlug($slug);
+
+        if (!$campaign) {
+            throw new \RuntimeException("Campaign not found: {$slug}");
+        }
+
+        // Check if user has already saved
+        $userHasSaved = $this->campaignService->hasUserSaved(
+            $campaign->id,
+            $session->getId()
+        );
+
+        // Prepare campaign data for view
+        $campaignData = [
+            'slug' => $campaign->slug,
+            'artist_name' => $campaign->artist_name,
+            'album_title' => $campaign->album_title,
+            'description' => $campaign->description,
+            'artwork_url' => $campaign->artwork_url,
+            'release_date' => $campaign->release_date?->format('F j, Y'),
+            'total_saves' => $campaign->total_saves,
+            'track_count' => $campaign->track_count,
+            'spotify_enabled' => (bool) $campaign->spotify_enabled,
+            'apple_music_enabled' => (bool) $campaign->apple_music_enabled,
+            'tracks' => $campaign->tracks ? array_map(
+                fn($track) => [
+                    'position' => $track->position,
+                    'title' => $track->title,
+                    'duration' => $track->duration ? $this->formatDuration($track->duration) : null,
+                    'preview_url' => $track->preview_url,
+                ],
+                $campaign->tracks
+            ) : null,
+        ];
+
+        return new ViewResult(
+            'campaign-landing',
+            new MetaData(
+                title: $campaign->artist_name . ' - ' . $campaign->album_title,
+                description: $campaign->description ?? 'Pre-save this album on Spotify',
+            ),
+            data: [
+                'campaign' => $campaignData,
+                'user_has_saved' => $userHasSaved,
+                'csrf_token' => $session->csrf->generateToken('campaign-landing')->toString(),
+            ]
+        );
+    }
+
+    private function formatDuration(int $seconds): string
+    {
+        $minutes = floor($seconds / 60);
+        $remainingSeconds = $seconds % 60;
+
+        return sprintf('%d:%02d', $minutes, $remainingSeconds);
+    }
+}