fix: auto-scale Y-axis, increase chart window to 200 points, add test…

[a-lie101]

What?

Fixed chart Y-axis scaling and increased data window size for the signal graph chart view.

How?

• Changed Y-axis domain from hardcoded [0, 100] to ['auto', 'auto'] to reflect real EEG data (±1000)
• Removed hardcoded ticks prop that was conflicting with auto-scaling
• Increased useNodeData chart window from 20 to 200 points
• Added /test-chart page for local CSV testing without a backend connection

Testing

• Loaded real EEG CSV (export.csv) via test page and confirmed all 4 signals render correctly at proper scale
• Verified table displays most recent rows correctly