Route the bull's hits through the typed DamageEvent pipeline

Hitbox now builds a DamageEvent (cause + hit position + shaped knock-up) and
calls the bull's new receive_damage(), instead of two stringly Object.call()s.
receive_damage adapts over the existing pip/knock-up logic so behaviour is
identical -- the characterization test drives both the string and typed paths
and asserts the same outcomes. Wire fx/damage/harness tests into run_tests.sh
+ CLAUDE.md. All hitbox guard tests green (stab, bear hitbox, ram, charge).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CmG3mQGVXZUPDVapmdbWZ1

CLAUDE.md

@@ -108,6 +108,9 @@ bash run_tests.sh
 # Individual tests:
 gdlint *.gd levels/*.gd tests/*.gd                                # GDScript lint (gdtoolkit, installed via uv)
 godot --headless --script tests/logic_test.gd         # pure logic, ~2 s
+godot --headless --script tests/harness_selftest.gd   # shared test_helpers: seeded RNG + approx + tally, ~1 s
+godot --headless --script tests/damage_pipeline_test.gd # bull's hit reception (take_sword_hit + typed receive_damage/DamageEvent), ~3 s
+godot --headless --script tests/fx_gallery_test.gd    # every registered Fx effect spawns + self-frees, ~2 s
 godot --headless --script tests/performance_test.gd   # frame-budget regression guard, ~4 s
 godot --headless --script tests/ragdoll_perf_test.gd  # on-hit spike breakdown: ragdoll build / sim-start / blood / mass hit, ~90 s
 godot --headless --script tests/gameplay_test.gd      # full scene, bone sanity, ~4 s