feat(research,cli,docs): state cost and risk knob units in introspect and the glossary

campaign introspect --unwired now annotates the four silently
misreadable knobs with unit/semantics sub-lines: cost_per_trade is a
price-unit numerator charged as cost/|entry−stop| in R (not a cost in
R); slip_vol_mult multiplies the per-cycle vol estimate; vol.length
smooths the estimator and does not set the stop's timescale; vol.k
scales the stop distance (the risk-unit lever). Rendered additively
via a new OpenSlot.notes field, so the sibling tests pinning the slot
hint lines verbatim stay green byte-identically.

The glossary's cost-model and risk-regime entries mirror the same
semantics inline (two-sentence convention kept), the risk entry
pointing at #262 for the timescale-matched variant.

closes #265

crates/aura-cli/src/research_docs.rs

@@ -278,6 +278,9 @@ fn describe_one_block(id: &str) -> Result<(), String> {
 fn print_open_slots(slots: &[aura_research::OpenSlot]) {
     for s in slots {
         println!("open slot: {} ({})", s.path, s.hint);
+        for note in &s.notes {
+            println!("    {note}");
+        }
     }
     if slots.is_empty() {
         println!("no open slots");