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.

manifest.json

@@ -1,12 +1,12 @@
 {
   "manifest_version": 3,
   "name": "ISMIS Helper",
-  "version": "1.3.0",
+  "version": "1.4.0",
   "description": "Auto-login, auto-accept privacy policy, and Study Load PDF for the USC ISMIS portal.",
   "permissions": ["storage", "downloads"],
   "host_permissions": ["https://ismis.usc.edu.ph/*"],
   "background": {
-    "scripts": ["libs/fontkit.min.js", "libs/pdf-lib.min.js", "pdf.js", "background.js"]
+    "scripts": ["libs/fontkit.min.js", "libs/pdf-lib.min.js", "pdf.js", "export-csv.js", "export-json.js", "export-xlsx.js", "background.js"]
   },
   "content_scripts": [
     {