Merge master into fix/submission-grader-grading-states-567

#578 (widget i18n/colour semantics) and #575 (missing-data display) both
rewrote submission-grader/widget.tsx, so every hunk of this branch
conflicted. Resolved by resetting the file to master and re-applying the
#567 fix on top of the new structure rather than reconciling markers.

What changed in the re-application:

- The three new affordances are now translated. "Not graded",
  "Teacher adjusted", the low-confidence pill and the ungraded-points note
  all have en/es entries in this widget's STRINGS table, matching #578's
  convention; a missing Spanish string is a type error.
- The em dash for an ungraded question is no longer hand-written.
  fmt.number() from shared/i18n.tsx already renders null as an em dash, so
  dropping the `?? 0` is now the entire fix at that call site and the
  dash follows the reader's locale like every other number.
- Points and confidence go through fmt.number/fmt.percent, so es renders
  "confianza: 41 %" rather than a hardcoded English percentage.

master's own shared/severity.ts landed the same rule this issue is about —
"a draft course with no lessons has nothing to complete (neutral); a
student who has completed nothing is at 0% and that is the worst case" —
and #575 applied it to the roster while leaving `points_earned ?? 0` in
this widget untouched. The re-applied fix is that doctrine reaching the
per-question list, and isUngraded() now cites it.

Kept from master unchanged: the inline "(82% confidence)" suffix for a
confident score, so only a guess is promoted to a pill.

Verified after the merge: mcp-server tsc --noEmit clean (the 4 pre-existing
useCallTool errors this branch flagged are gone — master fixed them),
66/66 mcp-server tests, and the demo fixture re-shot in dark, light and es.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Zt1kZKdcWAcsiJdBgnX3D

Author: guillermoscript

app/[locale]/layout.tsx

@@ -3,6 +3,7 @@ import { Geist, Geist_Mono, Noto_Sans } from "next/font/google";
 import "../globals.css";
 import { Toaster } from "@/components/ui/sonner";
 import { RouteProgress } from "@/components/shared/route-progress";
+import { FeedbackButton } from "@/components/shared/feedback-button";
 import { ThemeProvider } from "@/components/theme-provider";
 import { TenantProvider } from "@/components/tenant/tenant-provider"
 import { TenantCssVars } from "@/components/tenant/tenant-css-vars";
@@ -170,6 +171,7 @@ export default async function RootLayout({
               <TenantCssVars />
               <RouteProgress />
               {children}
+              <FeedbackButton />
               <Toaster />
             </TenantProvider>
           </ThemeProvider>