Register shape_dir_group_depth in telemetry opts schema

The StackSupervisor telemetry child passes :shape_dir_group_depth into ElectricTelemetry.StackTelemetry, but it was never added to the NimbleOptions schema. StackTelemetry therefore failed option validation at init, crashing the whole application on boot (surfaced as every integration test failing to start Electric).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: alco

packages/electric-telemetry/lib/electric/telemetry/opts.ex

@@ -5,6 +5,10 @@ defmodule ElectricTelemetry.Opts do
       installation_id: [type: :string],
       stack_id: [type: :string],
       storage_dir: [type: :string],
+      # Directory depth (relative to the disk-usage walk root) at which a single
+      # shape's directory sits, used to bucket the per-shape
+      # `electric.storage.dir.bytes` metric. `nil` disables per-shape grouping.
+      shape_dir_group_depth: [type: {:or, [:pos_integer, nil]}, default: nil],
       version: [type: :string, required: true],
       reporters: [
         type: :keyword_list,