Add Vue.js + uPlot UI migration to web/TODO.md

Notes Mainsail (Vue 3 + TypeScript + Vuetify, uPlot for live charts) as
the reference point for a future rewrite of app.js's hand-rolled DOM
wiring and the still-missing Automatic/Plot tab charts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0189FkmyJkY77HqsNomr1DwV

web/TODO.md

@@ -63,7 +63,23 @@ and checked against the Qt source side by side.
   an oversight - listed here too so this file alone is a complete picture
   of the gap. `SudForecastPlot`/`RealtimePlot`
   (`client/brewpi_gui.py:121-258`) are the reference for what each needs
-  to show.
+  to show. See the **uPlot** mention below - that's the leading candidate
+  for both.
+
+- [ ] **UI migration to Vue.js, charts via uPlot.** `app.js` is vanilla
+  JS with hand-rolled `document.getElementById`/`textContent` wiring for
+  every piece of state (see its own intro comment) - workable for v1's
+  scope, but every new feature (Pause, the Confirm `<dialog>`, ...) is
+  more manual DOM plumbing, and there's no charting at all yet (previous
+  item). Mainsail (the Klipper web UI - a comparable "control a piece of
+  hardware over a persistent WebSocket" app) is the reference point for
+  both: **Vue 3 + TypeScript + Vuetify** for reactive state-to-DOM
+  binding instead of this file's manual updates, and **uPlot** for live
+  charts specifically - it's canvas-based and fast enough for
+  high-frequency ticks (this server pushes `Elapsed`/`Ist` on every tick),
+  unlike heavier libraries like Chart.js. A bigger lift than anything
+  else in this file - revisit once the rest of this backlog (or at least
+  the charting item) makes it worth the rewrite, not before.
 
 - [ ] **No authentication.** Also already called out in README.md - matches
   the WebSocket server's own complete lack of it, not a new gap, but