🧠 Integrate notes.txt for dynamic thumbnail prompt generation

- Added generate_thumbnail_prompt(notes) to thumbnail_utils.py
- yt_poster.py now reads notes.txt (if present) from the clip directory
- Uses content to generate brand-aligned OpenAI prompt for future AI thumbnail generation
- Fallback: generic description if notes.txt is missing
- Prompt is printed for now; image generation hook is pending

modules/thumbnail_utils.py

@@ -0,0 +1,64 @@
+import subprocess
+import os
+from pathlib import Path
+
+def generate_thumbnail(video_path: str, output_path: str) -> str:
+    """
+    Generate a thumbnail image from the midpoint of the given video.
+
+    Parameters:
+        video_path (str): Path to the input video file.
+        output_path (str): Path where the thumbnail image (JPEG) should be saved.
+
+    Returns:
+        str: Path to the generated thumbnail image.
+
+    Notes:
+    - Uses FFmpeg to extract a frame using the 'thumbnail' filter.
+    - Thumbnail will be scaled to 1280x720 resolution (16:9).
+    - Overwrites the output file if it already exists.
+    """
+    video_path = Path(video_path)
+    output_path = Path(output_path)
+
+    if not video_path.exists():
+        raise FileNotFoundError(f"Video file not found: {video_path}")
+
+    output_path.parent.mkdir(parents=True, exist_ok=True)
+
+    cmd = [
+        "ffmpeg", "-y",  # Overwrite output if exists
+        "-i", str(video_path),
+        "-vf", "thumbnail,scale=1280:720",
+        "-frames:v", "1",
+        str(output_path)
+    ]
+
+    try:
+        subprocess.run(cmd, check=True)
+    except subprocess.CalledProcessError as e:
+        raise RuntimeError(f"Failed to generate thumbnail: {e}") from e
+
+    if not output_path.exists():
+        raise RuntimeError(f"Thumbnail was not created: {output_path}")
+
+    return str(output_path)
+
+
+def generate_thumbnail_prompt(notes: str) -> str:
+    """
+    Generate a rich thumbnail prompt from a descriptive sentence.
+
+    Args:
+        notes (str): A brief sentence describing the video content.
+
+    Returns:
+        str: A thumbnail generation prompt for OpenAI or DALL·E.
+    """
+    return (
+        f"Create a Fortnite-style gaming thumbnail based on the moment: \"{notes.strip()}\" "
+        f"featuring a stylized llama character with bold comic-style colors. Include dramatic or humorous elements "
+        f"(e.g., explosions, dance emotes, intense lighting), and text like 'HIGHLIGHT' or 'VICTORY ROYALE'. "
+        f"Use the Llama Chile Shop color palette (f7338f, 10abba, 1c0c38). The vibe should be fun, exaggerated, "
+        f"and chill — inviting viewers to laugh and enjoy the moment."
+    )