feat(movement): add movement state machine with air/ground/wallrun/slide/dash/ground states

- MovementStateMachine: core state machine base
- MovementParams: export-rich tunable resource
- StateGround/StateAir: grounded & aeriel locomotion with coyote, buffered jump, bunny hop
- StateWallRun / StateWallCling: wall-based traversal with wall-jump off
- StateSlide: sprint-parallel slide with friction fallout
- StateDash: burst dash with momentum brake
- PlayerMovementController: entry point wiring to CharacterBody3D
- input_map.cfg: full action map reference file
- characters/player/player_base.tscn: placeholder scene
- movement/tests/test_fsm_runner.gd: 9-state unit test runner

Closes #1

movement/states/state_slide.gd

@@ -0,0 +1,60 @@
+extends Node
+class_name StateSlide
+
+var machine: MovementStateMachine
+var params: MovementParams:
+	get: return machine.params
+
+var elapsed: float = 0.0
+
+
+func enter(_data: Dictionary = {}) -> void:
+	elapsed = 0.0
+	machine.register_chain_mechanic("slide")
+	# Lower player capsule
+	var player_node = machine.player
+	var shape: CapsuleShape3D = player_node.shape_owner_get_shape(0)
+	if shape:
+		shape.height = shape.height * 0.5
+
+
+func exit() -> void:
+	pass
+
+
+func update(delta: float) -> void:
+	elapsed += delta
+	var vel: Vector3 = machine.player.velocity
+	var forward: Vector3 = -machine.player.global_transform.basis.z
+	if forward.length_squared() > 1.0:
+		forward = forward.normalized()
+	vel.x = forward.x * params.slide_speed * machine.get_effective_speed(1.0)
+	vel.z = forward.z * params.slide_speed * machine.get_effective_speed(1.0)
+	vel.x *= pow(params.slide_friction, delta)
+	vel.z *= pow(params.slide_friction, delta)
+	machine.player.velocity = vel
+	machine.player.move_and_slide()
+
+	if machine.player.is_on_floor():
+		machine.on_ground = true
+		var speed := Vector3(vel.x, 0.0, vel.z).length()
+		if speed < params.slide_min_speed or elapsed > params.slide_duration:
+			var shape: CapsuleShape3D = machine.player.shape_owner_get_shape(0)
+			if shape:
+				shape.height = shape.height * 2.0
+			machine.register_chain_mechanic("slide_end")
+			machine.switch_to("ground")
+			return
+	else:
+		var shape2: CapsuleShape3D = machine.player.shape_owner_get_shape(0)
+		if shape2:
+			shape2.height = shape2.height * 2.0
+		machine.on_ground = false
+		machine.switch_to("air")
+
+	if not machine.input_crouch or not machine.input_sprint:
+		var shape3: CapsuleShape3D = machine.player.shape_owner_get_shape(0)
+		if shape3:
+			shape3.height = shape3.height * 2.0
+		machine.register_chain_mechanic("slide_cancel")
+		machine.switch_to("ground")