feat(v1.4.0): CSV/Excel/JSON/NextUp exports + hybrid smart year standing

- Export modules (export-csv/json/xlsx) mirroring the PDF layout, plus a
  Next Up import CSV matching the raycast/nextup column contract.
- Hybrid Year Level: View Grades history (exact per-semester standing),
  falling back to units math (prospectus total - lacking), then profile.
  Popup adds a year-mode setting (auto/custom/off).
- On-page button row now offers PDF / CSV / Excel / JSON / Next Up.
- Bump version to 1.4.0.
- Tag-only build workflow with an optional AMO sign step for a signed .xpi;
  separate ci.yml keeps tests on pushes/PRs.
- Tests: year-standing parser tests + export tests (CSV quoting, JSON schema,
  XLSX structure); CI validates XLSX via openpyxl.

background.js

@@ -10,28 +10,13 @@ function errMsg(err) {
   return String((err && err.message) || err);
 }
 
-// Build a download URL from PDF bytes. Firefox's background is a real page
-// (URL.createObjectURL available) and supports blob: URLs in downloads.
-// Chrome MV3 runs the background as a service worker where URL.createObjectURL
-// is NOT available, but its downloads API accepts base64 data: URLs.
-// Firefox rejects data: URLs in browser.downloads.download with
-// "Access denied for URL data:...", so pick per-browser.
-function buildDownloadUrl(bytes) {
-  if (typeof URL !== 'undefined' && typeof URL.createObjectURL === 'function') {
-    const blob = new Blob([bytes], { type: 'application/pdf' });
-    return URL.createObjectURL(blob);
-  }
-  // Fallback: Chrome MV3 service worker. PDFs here are small (~150KB), well
-  // within data-URL length limits.
-  let binary = '';
-  const chunk = 0x8000;
-  for (let i = 0; i < bytes.length; i += chunk) {
-    binary += String.fromCharCode.apply(null, bytes.subarray(i, i + chunk));
-  }
-  return 'data:application/pdf;base64,' + btoa(binary);
-}
-
 browser.runtime.onMessage.addListener((msg, sender, sendResponse) => {
+  if (msg && msg.type === 'export') {
+    runExport(msg.format, msg.data)
+      .then(() => sendResponse({ ok: true }))
+      .catch((err) => sendResponse({ ok: false, error: errMsg(err) }));
+    return true;
+  }
   if (msg && msg.type === 'generate-pdf') {
     generatePdf(msg.data)
       .then(() => sendResponse({ ok: true }))
@@ -40,6 +25,71 @@ browser.runtime.onMessage.addListener((msg, sender, sendResponse) => {
   }
 });
 
+// Generic downloader used by every export format. `filename` is used with
+// saveAs so the user picks the location, mirroring the PDF flow.
+async function downloadBytes(bytes, mime, filename, fallback) {
+  const safeFilename = filename || fallback;
+  const blob = new Blob([bytes], { type: mime });
+  const url = (typeof URL !== 'undefined' && typeof URL.createObjectURL === 'function')
+    ? URL.createObjectURL(blob)
+    : null;
+  let downloadUrl = url;
+  if (!downloadUrl) {
+    let binary = '';
+    const chunk = 0x8000;
+    for (let i = 0; i < bytes.length; i += chunk) {
+      binary += String.fromCharCode.apply(null, bytes.subarray(i, i + chunk));
+    }
+    downloadUrl = 'data:' + mime + ';base64,' + btoa(binary);
+  }
+  try {
+    const id = await browser.downloads.download({ url: downloadUrl, filename: safeFilename, saveAs: true });
+    const onChanged = (delta) => {
+      if (delta.id === id && delta.state && (delta.state.current === 'complete' || delta.state.current === 'interrupted')) {
+        browser.downloads.onChanged.removeListener(onChanged);
+      }
+    };
+    browser.downloads.onChanged.addListener(onChanged);
+  } catch (err) {
+    if (url) { try { URL.revokeObjectURL(url); } catch (e) {} }
+    throw err;
+  }
+}
+
+async function runExport(format, data) {
+  const header = data.header || {};
+  const year = parseInt(data.year, 10);
+  const period = formatPeriod(data.period || header.semester || '');
+  const compactProgram = ISMIStools.compactProgram(header.program || '');
+  const schoolYear = Number.isFinite(year) ? year + '-' + (year + 1) : '';
+  const core = [
+    header.studentId || (header.fullName ? header.fullName.replace(/\s+/g, ' ') : ''),
+    compactProgram,
+    schoolYear ? 'S.Y. ' + schoolYear : '',
+    period
+  ].filter(Boolean);
+  const base = core.join(' - ') || 'Study Load';
+
+  if (format === 'csv') {
+    const text = ISMIStools.buildStudyLoadCsv(data);
+    const bytes = new TextEncoder().encode(text);
+    await downloadBytes(bytes, 'text/csv', base + '.csv', 'Study Load.csv');
+  } else if (format === 'json') {
+    const text = JSON.stringify(ISMIStools.buildStudyLoadJson(data), null, 2);
+    const bytes = new TextEncoder().encode(text);
+    await downloadBytes(bytes, 'application/json', base + '.json', 'Study Load.json');
+  } else if (format === 'xlsx') {
+    const bytes = ISMIStools.buildStudyLoadXlsx(data);
+    await downloadBytes(bytes, 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet', base + '.xlsx', 'Study Load.xlsx');
+  } else if (format === 'nextup') {
+    const text = ISMIStools.buildNextUpCsv(data);
+    const bytes = new TextEncoder().encode(text);
+    await downloadBytes(bytes, 'text/csv', base + '-nextup.csv', 'Study Load - nextup.csv');
+  } else {
+    throw new Error('Unknown export format: ' + format);
+  }
+}
+
 function formatPeriod(period) {
   if (!period) return '';
   return String(period)
@@ -53,9 +103,6 @@ function formatPeriod(period) {
 
 async function generatePdf(data) {
   const bytes = await ISMIStools.buildStudyLoadPdf(data);
-  // Firefox accepts blob: object URLs; Chrome MV3 service worker has no
-  // URL.createObjectURL, so it falls back to a base64 data: URL there.
-  const url = buildDownloadUrl(bytes);
   const header = data.header || {};
   const year = parseInt(data.year, 10);
   const period = formatPeriod(data.period || header.semester || '');
@@ -70,17 +117,5 @@ async function generatePdf(data) {
   ].filter(Boolean);
   const filename = parts.join(' - ') + '.pdf';
   const fallback = 'Study Load - ' + (header.fullName || 'Student') + '.pdf';
-  const safeFilename = filename || fallback;
-
-  try {
-    const id = await browser.downloads.download({ url, filename: safeFilename, saveAs: true });
-    const onChanged = (delta) => {
-      if (delta.id === id && delta.state && (delta.state.current === 'complete' || delta.state.current === 'interrupted')) {
-        browser.downloads.onChanged.removeListener(onChanged);
-      }
-    };
-    browser.downloads.onChanged.addListener(onChanged);
-  } catch (err) {
-    throw err;
-  }
+  await downloadBytes(bytes, 'application/pdf', filename, fallback);
 }