feat(example): add interactive TUI training demo

Add demo_tui example with real-time visualization of the AttnRes
training process: loss curve (braille chart), depth attention weight
heatmap with actual alpha computation, pseudo-query norm growth bars,
and cycling algorithm step explainer. Uses ratatui + crossterm.

Adds layers() and embed_tokens() accessors to AttnResTransformer for
diagnostic extraction of attention weights during training.

Remove obsolete implementation_plan.md.

Author: AbdelStark

Cargo.lock

@@ -20,6 +20,8 @@ serde_json = "1"
 [dev-dependencies]
 proptest = "1"
 criterion = { version = "0.5", features = ["html_reports"] }
+ratatui = "0.29"
+crossterm = "0.28"
 
 [[bench]]
 name = "attn_res_benchmark"
@@ -36,3 +38,7 @@ path = "examples/compare_residuals.rs"
 [[example]]
 name = "visualize_weights"
 path = "examples/visualize_weights.rs"
+
+[[example]]
+name = "demo_tui"
+path = "examples/demo_tui.rs"