dashboard: pace a querying chart by its window, and an example to evaluate it

A chart is drawn in buckets, and nothing it can show changes until the
bucket it is drawing closes — so the resolution sets the refresh rather
than a flat five-second floor. A week at quarter-hour buckets now asks
four times an hour instead of sixty, for the same picture. Leaving the
field empty follows the window; a slower rate is still honoured.

`make seed-example` builds the thing to evaluate it with: a flow that
logs a temperature to InfluxDB, a flow that answers a chart's request by
turning the window into Flux and the rows back into a series, and a
dashboard holding the chart. The reading flow declares the request as an
input with a starting value, which is how a flow says a value reaches it
from a panel rather than from a node upstream.

Axis labels keep enough decimals to stay distinct — `si` rounds to three
figures, so every tick of a chart living inside one degree read "19".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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 test test-backend test-frontend soak lint lint-backend \
+        generate-client seed-example test test-backend test-frontend soak lint lint-backend \
         lint-frontend clean help
 
 COMPOSE_ROOT := $(CURDIR)
@@ -65,6 +65,9 @@ dev-frontend:  ## Start the Vite dev server (local)
 generate-client:  ## Regenerate the frontend SDK from the backend's OpenAPI schema
 	bash scripts/generate-client.sh
 
+seed-example:  ## Seed the querying-chart example (needs a running stack + InfluxDB)
+	cd backend && uv run python ../scripts/seed_example_chart.py
+
 # ── Testing ───────────────────────────────────────────────────────
 
 test: test-backend test-frontend  ## Run all tests (backend + frontend)