feat(progress): live status bar + % complete during exports

Adds a progress bar below the export buttons showing the current step
(reading table, fetching course descriptions i/N, profile, year level,
building file) with a 0-100% fill. Threads an onProgress callback through
scrapeStudyLoad and resolveYearLevel. Buttons disable during export to
prevent double-triggers; bar clears ~3s after success.

README.md

@@ -92,9 +92,12 @@ built `ismis-helper-chrome.zip` directly:
   - Year Level mode: `Auto` (recommended), `Use custom value`, or `Profile value
     only`.
 - **Smart Year Level**: for the semester being printed, `Auto` derives the
-  standing from the View Grades history (exact) or, failing that, from remaining
-  units (Student Prospectus total − Lacking Subjects). Custom value overrides;
-  the profile-scraped value is the fallback.
+  standing from remaining units (Student Prospectus total − Lacking Subjects,
+  reflecting units actually passed) or, failing that, from the View Grades
+  history. Custom value overrides; the profile-scraped value is the fallback.
+- **Live progress indicator**: during any export a status bar below the buttons
+  shows the current step (reading table, fetching course descriptions `i/N`,
+  profile, year level, building file) with a progress percentage.
 - **Next Up import**: the Next Up export writes CSV in the exact column contract
   the Raycast [Next Up](https://github.com/) extension accepts
   (`title, courseCode, days, startTime, endTime, room, units, professorName`),