Split long vertical chains into smaller clustered subgraphs

- Add subgraph cluster styling (style <id> fill:#HEX after each 'end')
- Split area_2 (Isle of Wonder) into 3 subgraphs: Gnomes, Garden & Beach, Chessboard & Trades
- Split area_3 (Isle of Beast) into 2 subgraphs: Approach & Maze, Dark Passage & Minotaur
- Split area_5 (SacRED MOUNTAIN) into 2 subgraphs: Cliffs/Cave/Poison, Spell Components
- Split area_7 (Realm of Dead) into 3 subgraphs: Arrival & Zombies, Gate & Charon, Death & Return

Total subgraphs increased from 8 to 14 for better line clustering.
Lines now average ~10-15 nodes per subgraph instead of 30-60.

Also update skills:
- Document subgraph cluster styling requirement (style <id> after 'end')
- Add cluster size guidance (aim for 10-20 nodes per subgraph)

.opencode/skills/create-dependency-graph/SKILL.md

@@ -268,6 +268,13 @@ end
 - Include Phase 1, Phase 2, etc. all under the same area subgraph
 - Exception: If same area appears at very different logical points (start vs end), use separate subgraphs with same color
 
+**Cluster Size and Line Length**:
+- **Keep clusters small**: Aim for 10-20 nodes per subgraph maximum
+- **Avoid long vertical stretches**: If a subgraph has 40+ nodes vertically, break it into multiple smaller subgraphs
+- **Shorter lines = better readability**: Cluster related nodes together
+- **When to split**: If lines would stretch more than ~15 nodes vertically, create a new subgraph
+- **Trade-off**: More subgraphs with fewer nodes each is better than few subgraphs with long chains
+
 #### Subgraph Styling Format
 
 Use this exact format for subgraph titles to ensure proper font size:
@@ -277,8 +284,11 @@ subgraph area_name["<style>subgraphTitleTitle {font-size: 18px; font-weight: bol
     classDef area_X fill:#HEXCOLOR,stroke:#STROKECOLOR,stroke-width:2px
     class node1,node2,node3 area_X
 end
+style area_name fill:#HEXCOLOR,stroke:#STROKECOLOR,stroke-width:3px
 ```
 
+**IMPORTANT**: The `style <subgraph_id>` command MUST come AFTER the `end` of the subgraph to color the container/cluster itself. Without this, the subgraph background won't be visible.
+
 #### Color-Coded Areas (Index-Based)
 
 Apply index-based palette: