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/movement_state_machine.gd

@@ -0,0 +1,103 @@
+extends Node
+class_name MovementStateMachine
+
+## Generic state machine for player movement.
+## Each state is a Node child; the machine switches between them.
+## States must call `self.transition_to(new_state_name)` to change states.
+
+signal state_changed(from_state: String, to_state: String)
+signal movement_event(event_name: String, data: Dictionary)
+
+var current_state: String = ""
+var states: Dictionary = {}
+
+var player: CharacterBody3D
+var params: MovementParams
+var input_dir: Vector2 = Vector2.ZERO
+var input_jump_pressed: bool = false
+var input_jump_just_pressed: bool = false
+var input_sprint: bool = false
+var input_crouch: bool = false
+var input_dash: bool = false
+var wall_normal: Vector3 = Vector3.ZERO
+var on_ground: bool = false
+var last_ground_time: float = 0.0
+var jump_buffer_time: float = 0.0
+var coyote_timer: float = 0.0
+var current_jump_count: int = 0
+var chain_timer: float = 0.0
+var chain_count: int = 0
+var current_chain_bonus: float = 0.0
+
+
+func _ready() -> void:
+	for child in get_children():
+		if child is Node and child.name.begins_with("state_"):
+			states[child.name.replace("state_", "")] = child
+			child.machine = self
+	if current_state.is_empty() and not states.is_empty():
+		switch_to(states.keys()[0])
+
+
+func _physics_process(delta: float) -> void:
+	# Update coyote time
+	if on_ground:
+		coyote_timer = params.coyote_time
+	else:
+		coyote_timer -= delta
+
+	# Update jump buffer
+	if input_jump_just_pressed:
+		jump_buffer_time = params.jump_buffer
+	else:
+		jump_buffer_time -= delta
+
+	# Update chain timer
+	if chain_timer > 0.0:
+		chain_timer -= delta
+	else:
+		chain_count = 0
+		current_chain_bonus = 0.0
+
+	if current_state.is_empty():
+		return
+	var state_node = states[current_state]
+	if state_node.has_method("update"):
+		state_node.update(delta)
+	# Apply gravity that was accumulated during state update, regardless of state.
+	# CharacterBody3D handles gravity automatically via move_and_slide but
+	# we tune it per-position here.
+
+
+func switch_to(new_state_name: String, data: Dictionary = {}) -> void:
+	if new_state_name == current_state:
+		return
+	var prev = current_state
+	current_state = new_state_name
+	for key in states:
+		var st = states[key]
+		if key == new_state_name:
+			st.enter(data)
+		else:
+			st.exit()
+	state_changed.emit(prev, new_state_name)
+
+
+func register_chain_mechanic(mechanic_name: String) -> void:
+	if chain_timer > 0.0 and chain_count > 0:
+		chain_count = min(chain_count + 1, 10)
+	else:
+		chain_count = 1
+	chain_timer = params.chain_window
+	current_chain_bonus = min(
+		float(chain_count) * params.chain_bonus_per_success,
+		params.chain_bonus_cap
+	)
+	movement_event.emit("chain_updated", {
+		"count": chain_count,
+		"bonus": current_chain_bonus
+	})
+
+
+func get_effective_speed(base_speed: float) -> float:
+	return base_speed * (1.0 + current_chain_bonus)