feat(VI-5): rich CLI dashboard with sparklines, stats, and color

[dnacenta]

Summary

• Sparkline graphs (▁▂▃▄▅▆▇█) showing signal history over time
• Color-coded signal values based on health thresholds (green/yellow/red)
• Statistics section: mean, standard deviation, percentile rank, streak detection
• Anomaly detection: flags readings 2+ std devs from baseline with rarity indicators
• --json flag for machine-readable output
• Migrated all raw ANSI escape codes to owo-colors crate (zero-allocation, modern)
• New stats.rs module with 15 unit tests

Example output

  Signals
    vocabulary diversity   0.35  █████████▁▁▁▁▁▁▁▁▁▁▁  →  -0.00
    question generation    6.00  ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄  →  +0.00
    thought lifecycle      0.20  ▁▁▁▁▁▁▁▁▁███████████  →  +0.00
    evidence grounding     0.82  ▁▁▁▁▁▁▁▁▁███████████  →  +0.00

  Statistics
    vocabulary diversity   mean 0.36  sd 0.01  pctl  28%  streak =28
    question generation    mean 6.00  sd 0.00  pctl  50%  streak =50
    thought lifecycle      mean 0.11  sd 0.10  pctl  72%  streak =28
    evidence grounding     mean 0.81  sd 0.01  pctl  72%  streak =28

Closes #5