Add feed deletion and single video addition features

- Implemented DELETE /api/channels/<id> to remove channels and cleanup downloaded files
- Added delete button to channels page with confirmation dialog
- Added functionality to add single videos via URL
- Updated navigation menu

templates/add_video.html

@@ -0,0 +1,55 @@
+{% extends "base.html" %}
+
+{% block title %}Add Video - YottoB{% endblock %}
+
+{% block content %}
+<div class="add-video-page">
+    <div class="page-header">
+        <h2>Add Individual Video</h2>
+        <p>Add a specific YouTube video to your library</p>
+    </div>
+
+    <div class="form-container">
+        <form method="POST" action="/add-video" class="channel-form">
+            <div class="form-group">
+                <label for="video_url">YouTube Video URL</label>
+                <input
+                    type="url"
+                    id="video_url"
+                    name="video_url"
+                    placeholder="https://www.youtube.com/watch?v=VIDEO_ID"
+                    required
+                    class="form-input"
+                >
+                <small class="form-help">
+                    Enter the full YouTube video URL.
+                </small>
+            </div>
+
+            <div class="form-actions">
+                <button type="submit" class="btn btn-primary">Add Video</button>
+                <a href="/" class="btn btn-secondary">Cancel</a>
+            </div>
+        </form>
+    </div>
+
+    <div class="help-section">
+        <h3>How to add a video</h3>
+        <ol>
+            <li>Go to the YouTube video you want to add</li>
+            <li>Copy the URL from your browser's address bar</li>
+            <li>Paste it into the form above</li>
+            <li>Click "Add Video"</li>
+        </ol>
+
+        <h4>Supported URL formats</h4>
+        <ul>
+            <li><code>https://www.youtube.com/watch?v=VIDEO_ID</code></li>
+            <li><code>https://youtu.be/VIDEO_ID</code></li>
+        </ul>
+
+        <h4>Note</h4>
+        <p>YouTube Shorts are not supported and will be rejected.</p>
+    </div>
+</div>
+{% endblock %}