M6.10: Leporidae trait restoration + HP math fix

Replace clade traits with the doc-canonical trio: Burst Speed (40 ft.
base + bonus-action Dash, prof-bonus uses), Tremor Sense (detect
ground-vibrating creatures within 30 ft.), Lucky Feet (reroll a 1
on a save, 1/short rest). Drop the misplaced Leaping Strides /
Burrow Savvy / Twitch Reflexes — those were thinner substitutes.

Detriments: Fragile Build now correctly halves to -2 HP/level (was
-1). Add Panic Cascade — forced-Dash on bad fear save, contagious to
allied Leporidae within 15 ft. Drop Constant Vigilance, which was
not in the doc.

Bump Rabbit-Folk base_speed_ft to 40 to match Burst Speed's clade
default. Hare-Folk stays at 45 (its species trait Open Ground Runner
sets that explicitly).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Content/Data/species.json

@@ -223,7 +223,7 @@
     "name": "Rabbit-Folk",
     "size": "small",
     "ability_mods": { "WIS": 1 },
-    "base_speed_ft": 30,
+    "base_speed_ft": 40,
     "traits": [
       { "id": "warren_dweller",        "name": "Warren Dweller",        "description": "Burrow speed 10 ft. through loose soil. Advantage on Stealth checks in your home warren. Community Resilience: once per long rest, when within 30 ft. of two or more allies, regain 1d4 + level HP." },
       { "id": "powerful_legs",         "name": "Powerful Legs",         "description": "Standing long jump distance equals your speed; running long jump doubles it." }