Add per-user learned machine profile; fix methodology honesty issues

Replaces the flat additive batch-size correction with a per-user
multiplicative pace factor learned from each account's own logged
roasts (shared/learn.js, GET /api/machine-profile), plus a lot-scoped
"last refine" auto-suggestion. Also fixes the reference data being
framed as "your own roasts" on a now-multi-user product, and
reclassifies the drying/Maillard sanity checks as informational since
they're algebraically derived from the DTR check rather than
independent (yellow = 0.56 x first crack, not entered separately).

Bug fixes found by an adversarial Opus review of the first pass:
- Unicode minus sign (U+2212) broke duration parsing against the
  app's own generated refine-suggestion text
- Printed sanity-checks table still showed a bare pass/fail glyph for
  the now-informational drying/Maillard rows
- Printed time-ledger box didn't show the pace multiplication step,
  so it stopped reconciling by hand once pace != 1
- Field 6.4 (manual batch correction) was double-counted: excluded
  from the learned-pace fit but added back after the multiplication
- Learned pace had no outlier rejection or hard clamp
- computeLedger had no test coverage
- Batch-size help copy overstated what the pace factor models (it's
  a single blanket ratio, not conditioned on batch weight)

A follow-up Opus pass also caught the per-user profile cache
surviving logout/account-switch in a shared browser; fixed by
sweeping it alongside the existing plan-draft cleanup.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

public/js/field-help.js

@@ -4,7 +4,7 @@
 
 import { HELP_TOPICS } from "./field-help-content.js";
 
-export function initFieldHelp({ getPlan, getTempUnit }) {
+export function initFieldHelp({ getPlan, getTempUnit, getMachineProfile }) {
 	const dialog = document.getElementById("field-help-dialog");
 	if (!dialog) return;
 	const titleEl = document.getElementById("help-dialog-title");
@@ -16,7 +16,7 @@ export function initFieldHelp({ getPlan, getTempUnit }) {
 		if (!topic) return;
 		lastTrigger = trigger;
 		titleEl.textContent = topic.title;
-		bodyEl.replaceChildren(topic.render(getPlan(), getTempUnit?.()));
+		bodyEl.replaceChildren(topic.render(getPlan(), getTempUnit?.(), getMachineProfile?.()));
 		bodyEl.scrollTop = 0;
 		dialog.showModal();
 	}