gmp(M02): add player input intent seam

Work-Package: M02-GMP-INPUT-001
Agent: sindo-main-codex
Tests: verify_player_input; renderer baseline dry-run; coordinate, streaming, documentation and coordination gates
Fidelity: preserves current sandbox bindings and movement/camera behavior; exact build-12340 semantics remain unverified

src/gameplay/input/player_input_source.gd

@@ -0,0 +1,45 @@
+class_name PlayerInputSource
+extends RefCounted
+
+## Converts remappable Godot Input Map actions into immutable [MoveIntent] values.
+## This adapter owns no movement state and may be replaced independently of the
+## local movement controller.
+
+
+## Samples the current Input singleton state for one physics tick.
+func sample_move_intent() -> MoveIntent:
+	return compose_move_intent(
+		Input.get_action_strength(PlayerInputActions.MOVE_FORWARD),
+		Input.get_action_strength(PlayerInputActions.MOVE_BACKWARD),
+		Input.get_action_strength(PlayerInputActions.STRAFE_LEFT),
+		Input.get_action_strength(PlayerInputActions.STRAFE_RIGHT),
+		Input.get_action_strength(PlayerInputActions.DEBUG_FLY_UP),
+		Input.get_action_strength(PlayerInputActions.DEBUG_FLY_DOWN),
+		Input.is_action_pressed(PlayerInputActions.DEBUG_SPRINT)
+	)
+
+
+## Builds a normalized intent from action strengths for deterministic tests and
+## alternative input adapters. Strengths outside `[0, 1]` are clamped.
+static func compose_move_intent(
+		forward_strength: float,
+		backward_strength: float,
+		strafe_left_strength: float,
+		strafe_right_strength: float,
+		fly_up_strength: float,
+		fly_down_strength: float,
+		sprint_requested: bool
+) -> MoveIntent:
+	var planar_axis := Vector2(
+		clampf(strafe_right_strength, 0.0, 1.0) - clampf(strafe_left_strength, 0.0, 1.0),
+		clampf(forward_strength, 0.0, 1.0) - clampf(backward_strength, 0.0, 1.0)
+	)
+	if planar_axis.length_squared() > 1.0:
+		planar_axis = planar_axis.normalized()
+	var vertical_axis := clampf(fly_up_strength, 0.0, 1.0) - clampf(fly_down_strength, 0.0, 1.0)
+	return MoveIntent.new(
+		planar_axis.y,
+		planar_axis.x,
+		vertical_axis,
+		sprint_requested
+	)