Keep the theme redraw from wiping a chart's x scale

Reaching Home from another page builds its charts in the same commit their
theme effect first fires in, with the readings already cached. uPlot ranges its
scales in a microtask, so `redraw()` re-set the x scale from the chart's own —
still empty — bounds before that ran, and the pending range taken from the data
was lost: axes without ticks, no lines, and no way back but the range control,
which rebuilds the chart. Redrawing without the paths is all a colour swap
needs and leaves the scales alone.

The cards also carried "Nothing has run yet." while the first readings were
still on their way; they now carry the skeleton the rest of Home uses.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SKL7sUgNWhukDEz95vSMQv

NOTEPAD.md

@@ -13,7 +13,6 @@ should reopen it.
 
 ### To be sorted
 
-- BUG/UI the "Failures and Timing" and "Throughput per Minute" figures don't show any data upon intial load (and no loading indicator). Selecting a time range seems to trigger redraw and resolves it
 - BUG/UI when enlarging the code editor of a node, the code editor should enlarge to the left (node settings remain on the right) so that the code editor fills the center of the screen with the node properties available next to it
 - BUG/UX the console/log panel does not show print output of nodes
 - CHORE/UI: loop lag on Home reads a real number with no flows, and that is right — `LoopWatchdog` times how late `asyncio.sleep(1.0)` wakes on the API's event loop and is started unconditionally, so it measures the engine process rather than any flow, and it is what turns the health badge `degraded`. Nothing to fix; recorded so it is not reopened.