feat: radial social graph visualization

[barrydeen]

Summary

• Replace plain text stats in the Social Graph screen with a radial visualization showing profile pictures in concentric rings
• Center ring: current user (56dp, highlighted with glow), inner ring: ~8 first-degree follows (36dp), outer ring: ~14 qualified 2nd-degree users (28dp)
• Curved Bezier connection lines drawn on Canvas with gradient alpha fade using theme colors
• Nodes with cached profile pictures are prioritized; outer ring nodes clustered near the inner node that follows them
• Stats summary and Recompute button retained below the visualization
• Added Social Graph entry to the navigation drawer under Settings

Test plan

• Open drawer → Settings → Social Graph
• With cached graph: verify circular visualization with profile pictures and connection lines
• Without cache: verify "not computed" state with Compute button
• Tap Recompute → progress states → Complete → Done → updated visualization
• Verify scroll works if content exceeds screen height