Add the hosted-demo seed: a house panel over three flows

`scripts/seed_demo.py` wipes and recreates one persistent demo — `home`,
`home_history` and `pv_model`, plus a `demo` dashboard carrying all fifteen
widget types across three sections. Operational script for the hosted
instance only: `make seed-hosted-demo`, with `API_URL` selecting which one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HTsT1isxUjw5gtkJk8WhuA

Makefile

@@ -3,7 +3,7 @@
 # The workspace root delegates to these (see ../Makefile).
 
 .PHONY: dev-utils dev dev-local up down update install dev-backend dev-frontend \
-        generate-client seed-example seed-demo test test-backend test-frontend soak bench-startup lint lint-backend \
+        generate-client seed-example seed-demo seed-hosted-demo test test-backend test-frontend soak bench-startup lint lint-backend \
         lint-frontend umami clean help
 
 COMPOSE_ROOT := $(CURDIR)
@@ -97,6 +97,20 @@ seed-example:  ## Seed the querying-chart example (needs a running stack + Influ
 seed-demo:  ## Seed the training-run example: a batch flow and its dashboard
 	cd backend && uv run python ../scripts/seed_demo_training.py
 
+# Operators of the hosted demo only — NOT part of any deployment, and nothing a
+# self-hosted instance needs. It wipes and recreates its three flows and its
+# dashboard, so re-running it is how the public demo is reset.
+# `uv run` does not read .env, so the credentials are lifted out of it here;
+# anything already exported wins, which is how a remote instance is targeted:
+#   API_URL=https://api.example.com make seed-hosted-demo
+seed-hosted-demo:  ## Seed the hosted demo panel (operators only; API_URL selects the instance)
+	@user=$$(grep -E '^FIRST_SUPERUSER=' $(COMPOSE_ROOT)/.env 2>/dev/null | head -1 | cut -d= -f2-); \
+	pass=$$(grep -E '^FIRST_SUPERUSER_PASSWORD=' $(COMPOSE_ROOT)/.env 2>/dev/null | head -1 | cut -d= -f2-); \
+	cd backend && \
+	  FIRST_SUPERUSER="$${FIRST_SUPERUSER:-$$user}" \
+	  FIRST_SUPERUSER_PASSWORD="$${FIRST_SUPERUSER_PASSWORD:-$$pass}" \
+	  uv run python ../scripts/seed_demo.py
+
 # ── Testing ───────────────────────────────────────────────────────
 
 test: test-backend test-frontend  ## Run all tests (backend + frontend)