docs: record, verify, and sync ENH-010 graduation thesis grade feature

[ffooll-bit]

Summary

Records, verifies, and syncs improvement ENH-010 — allowing a missing thesis/skripsi grade to be filled in at the end of the PISN Graduation wizard.

• docs: record ENH-010 — logs the idea (problem: a thesis course can exist in the transcript with no grade and the wizard offers no way to fill it; fix plan: a new Excel column holding the letter grade, shown on the transcript step, pushed at finish).
• docs: verify ENH-010 — deep-verified against the app code and the live Neo Feeder WS GetDictionary. Confirmed the UpdateNilaiPerkuliahanKelas act: composite key id_registrasi_mahasiswa + id_kelas_kuliah, record carrying nilai_huruf/nilai_angka/nilai_indeks. Both key values (id_reg_pd, id_kls) are available directly on the cloud nilai_mahasiswa thesis row (verified live), so no extra lookup is needed. Actual Fix updated accordingly.
• docs: sync ENH-010 issue #110 into tracker — records the GitHub issue number on the tracker item.

This is documentation-only (tracker file docs/IMPROVEMENTS.md). No application code is changed.

Checklist

• php -l passes on all modified PHP files (no PHP changed)
• No unrelated files changed (only docs/IMPROVEMENTS.md, plus the new GitHub issue Graduation wizard: allow filling in a missing thesis grade #110)
• Tracker follows the Findings & Planning workflow (each interaction committed once on docs/improvements)

Notes for reviewers

The associated change will be implemented by the Code Implementation workflow. The referenced issue (#110) is intentionally left open here and will be closed when implemented.