Sync Canvas LMS export feature + refreshed Settings screenshot

Brings the share build up to date with the main project: QTI .zip export
and optional direct Canvas API push, plus the Canvas settings card.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -88,6 +88,23 @@ Open **<http://localhost:3000>**. This variant uses host networking, so the cont
 
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+## Export to Canvas (LMS)
+
+Turn any assignment into a real Canvas quiz. In the editor, choose **Export → Canvas (LMS)**. Title, description, points, and every question are filled in automatically and mapped to the right Canvas question type (multiple choice, true/false, essay, fill-in-the-blank, matching). Optional quiz settings — type, time limit, attempts, dates, shuffle, access code — are right there in the dialog with sensible defaults.
+
+![Canvas export dialog](docs/screenshots/canvas-export-dialog.png)
+
+Two ways to get it into Canvas:
+
+- **Download a `.zip`** (works on every Canvas, no login) — then in Canvas: **Settings → Import Course Content → QTI .zip file**.
+- **Send it directly** into a course — add your Canvas web address and a personal access token once under **Settings → Canvas (LMS) integration**, and the dialog gains a course picker that creates the quiz for you (as an unpublished draft you review first).
+
+![Canvas integration settings](docs/screenshots/canvas-settings.png)
+
+> Short-answer and essay questions import as manually-graded Canvas questions. Discussion-style prompts have no Canvas quiz equivalent, so they're left out of the quiz (you'll see a note in the dialog). A case-study passage becomes an intro block at the top.
+
+---
+
 ## Where is my data?
 
 Everything — assignments, settings, API keys, your school logo — lives in a single JSON file inside the `assignment-data` Docker volume. It survives restarts, rebuilds, and image upgrades.