fix(spells): correct the sound burst save

PF1e (SRD spells/sound-burst.md): "Every creature in the area takes 1d8 points of sonic damage and must succeed on a Fortitude save to avoid being stunned for 1 round" — the Fortitude partial negates the stun only, never the dice. The damage component declared half_on_save: true, halving the sonic damage on a successful save. DamageEffect gains a save_negates flag (default True, existing behavior unchanged); sound_burst.json declares half_on_save: false + save_negates: false so the 1d8 is full regardless while the condition keeps save_negates. README updated.

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

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

data/spells/sound_burst.json

@@ -10,13 +10,14 @@
     {
       "type": "area",
       "radius_ft": 10,
-      "save_for_half": true,
+      "save_for_half": false,
       "effects": [
         {
           "type": "damage",
           "formula": "1d8",
           "types": ["sonic"],
-          "half_on_save": true
+          "half_on_save": false,
+          "save_negates": false
         },
         {
           "type": "condition",
@@ -27,5 +28,5 @@
       ]
     }
   ],
-  "description": "A tremendous cacophony blasts a 10-ft.-radius spread: every creature in the area takes 1d8 points of sonic damage and must succeed on a Fortitude save or be stunned for 1 round (Fortitude partial — modeled as save for half damage and negates the stun). Creatures that cannot hear take the damage but are not stunned (not modeled)."
+  "description": "A tremendous cacophony blasts a 10-ft.-radius spread: every creature in the area takes 1d8 points of sonic damage and must succeed on a Fortitude save to avoid being stunned for 1 round (SRD spells/sound-burst.md: the save only negates the stun - the damage is full regardless). Creatures that cannot hear take the damage but are not stunned (not modeled)."
 }