docs(rules): document the bladed dash approximation

Bladed Dash's description now matches the SRD (standard action, move up
to 30 ft in a straight line without provoking attacks of opportunity,
single melee attack at highest BAB against any creature adjacent along
the path) and the README's spell-limits section records the engine
approximation: a +30 ft speed buff for 1 round, with the free melee
attack, the no-AoO movement, the straight-line constraint and the
circumstance attack bonus left unmodeled.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

README.md

@@ -1585,6 +1585,15 @@ Limites de sorts (conformance D6-D9, documentées plutôt que bricolées) :
   modélisé, S1a/S1c) : la sauvegarde partielle est désormais modélisée (panic
   à l'échec, `shaken` 1 round au succès — voir « Sauvegardes partielles » plus
   bas) ; seule la durée « 1 round/niveau » du `panicked` reste fixée à 4 rounds.
+- **Bladed Dash — approximation** (SRD spells/bladed-dash.md : « When you cast
+  this spell, you immediately move up to 30 feet in a straight line any
+  direction [...] This movement does not provoke attacks of opportunity. You
+  may make a single melee attack at your highest base attack bonus against any
+  creature you are adjacent to at any point along this 30 feet ») : le sort est
+  modélisé comme un buff de vitesse +30 ft pour 1 round ; l'attaque de mêlée
+  gratuite, le déplacement sans AoO, la contrainte de ligne droite et le bonus
+  de circonstance à l'attaque (mod d'Int ou de Cha, le plus élevé) ne sont pas
+  modélisés.
 
 ## Architecture
 

data/spells/bladed_dash.json

@@ -15,5 +15,5 @@
       "duration_rounds": 1
     }
   ],
-  "description": "You move up your speed as a move action and make one melee attack at the end. Simplified as a +30 ft speed buff for 1 round; the extra attack is not modeled."
+  "description": "Upon casting, you immediately move up to 30 feet in a straight line in any direction; this movement does not provoke attacks of opportunity, and you may make a single melee attack at your highest base attack bonus against any creature you are adjacent to at any point along this 30 feet (SRD bladed dash). Simplified as a +30 ft speed buff for 1 round; the free melee attack, the no-AoO movement, the straight-line constraint and the circumstance attack bonus are not modeled."
 }