docs: define CDN capabilities and P2P federation in goals.md

Added a detailed specification for CDN functionality, including:
- Lightweight CDN node concept (simple executable for users)
- Secure connectivity using pre-shared keys
- Dynamic registration with main metadata server and DNS assignment
- Content awareness, replication, and streaming fallback
- Peer-to-peer (P2P) sharing for distributed content transfer
- Federation and collaboration between CDNs
- Future idea: predictive caching based on user activity

This formalizes the CDN architecture for Walros, supporting distributed caching,
federation, and smarter prefetching mechanisms."

goals.md

@@ -4,8 +4,44 @@
   - **Caching & Performance:**
     - Use cached segments for seamless seeking and fast resume.
     - If another user starts playback with the same parameters, reuse existing cached data to minimize transcoding and bandwidth usage.
-- **CDN capabilities and P2P federation**
+- **CDN Capabilities and P2P Federation**
-  - TODO: Define this feature in detail.
+  - **Lightweight CDN Node:**  
+    - Each CDN node runs as a standalone executable binary that can be easily deployed by both technical and non-technical users.  
+    - Minimal configuration required:
+      - **Data Directory:** Defines where cached media files are stored.  
+      - **Optional Name:** Human-readable CDN identifier (used for UI labeling and dynamic DNS registration).  
+      - **Mode:** Can operate as a **shared CDN** (available to multiple users) or a **local-only CDN**.  
+
+  - **Secure Connectivity:**  
+    - Each CDN connects to the **main metadata server** using a **pre-shared key** for authentication and trust establishment.  
+    - This ensures only authorized CDNs can register and exchange data with the main network.  
+
+  - **Dynamic Registration & Discovery:**  
+    - Upon startup, the CDN connects to the **main metadata server** and automatically registers itself.  
+    - The main server assigns a **dynamic DNS name** to each CDN for seamless connectivity.  
+    - CDNs periodically update their metadata to report available content, storage capacity, and health status.  
+
+  - **Content Awareness & Distribution:**  
+    - The main server maintains a global index of all available CDNs and the content cached on each.  
+    - Users can choose which CDN should serve their content in the client UI.  
+    - If a requested content is missing from the selected CDN, users have two options:
+      1. **Request content replication:** Copy or prefetch the content from another CDN or the main server.  
+      2. **Stream fallback:** Stream the content directly from the main server or the nearest available CDN.  
+
+  - **Peer-to-Peer (P2P) Sharing:**  
+    - CDNs and the main server interconnect via **P2P protocols** to simplify file transfer and reduce reliance on centralized infrastructure.  
+    - This enables faster, bandwidth-efficient distribution of popular content between geographically distributed CDNs.  
+
+  - **Federation & Collaboration:**  
+    - Multiple CDNs can share content and metadata within a trusted federation network.  
+    - The system can automatically balance or replicate popular content across CDNs to optimize bandwidth usage and ensure availability.  
+
+  - **Future Idea – Predictive Caching:**  
+    - CDNs may automatically pre-cache upcoming content based on user activity patterns.  
+      - If a user watches the first movie in a series, the CDN pre-fetches sequels (e.g., parts 2, 3, etc.).  
+      - If a user starts a new TV show, the CDN preloads subsequent episodes or seasons.  
+    - This predictive caching minimizes latency and improves the user experience by ensuring likely-next content is available instantly.  
+
 - **Metadata Management:**
   - Automatically identify and fetch metadata from databases like IMDb, TVDB, etc.
   - Allow users to edit and correct metadata manually.