chore: import upstream snapshot with attribution

examples/showcases/arcade-tools/.env.example

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+# --- Arcade -----------------------------------------------------------------
+# Create a key at https://api.arcade.dev/dashboard (or https://docs.arcade.dev)
+ARCADE_API_KEY=arc_...
+
+# Stable identifier for the end user Arcade acts on behalf of. In production,
+# set this per-request from your own auth/session instead of a single value.
+# For local testing, use the email you signed up to Arcade with.
+ARCADE_USER_ID=you@example.com
+
+# --- Model ------------------------------------------------------------------
+# CopilotKit's Built-in Agent calls this model. Key from platform.openai.com
+OPENAI_API_KEY=sk-...
+
+# Optional. Override the default model ("provider/model" or "provider:model").
+# OPENAI_MODEL=openai/gpt-4o
+
+# --- CopilotKit -------------------------------------------------------------
+# The CopilotKit runtime sends anonymous telemetry by default. Opt out here.
+COPILOTKIT_TELEMETRY_DISABLED=true
+
+# --- Security (see "Deploying publicly" in the README) ----------------------
+# The agent runtime can send/read email on your keys. Before any public or
+# multi-user deployment, protect /api/copilotkit. Setting this requires every
+# request to send `Authorization: Bearer <token>` (a starter gate; replace with
+# your real session auth). Leave unset for local dev.
+# COPILOTKIT_RUNTIME_TOKEN=
+
+# LOCAL EXPERIMENTS ONLY: lets the client pass `x-arcade-user-id` to scope tool
+# calls per user. Client headers are spoofable, so in production derive the user id
+# from a server-verified session instead. Leave unset.
+# ARCADE_ALLOW_HEADER_USER_ID=true