Unify certificate typography, justify body text, fix margins and semester labels

[vikrantwiz02]

Summary

• All four certificates (Bonafide, Fee, Demand Letter, Fee Structure) now share one consistent style: Caladea at 11pt for headings/labels/signatures, 12pt for the main certify-that body paragraph, and Carlito at 11pt for bulleted footnotes.
• Caladea/Carlito are metric-compatible, SIL Open Font License substitutes for Cambria/Calibri (the originals are proprietary Microsoft fonts and can't be redistributed in the repo), sourced from Google Fonts.
• Body text, table cells and signature lines are now justified instead of left-aligned.
• Page margins unified to 3.5cm top, 1.5cm left/right, 2cm bottom across all four.
• Fixed the Fee Structure Certificate's semester-pair table headers, which were hardcoded to "Semester-I"/"Semester-II" regardless of which semester pair was actually being issued (e.g. semester 7/8) — they now read the real odd/even semester numbers.

Test plan

• Syntax-checked with python -m ast
• Generated real PDFs end-to-end (Bonafide, Fee Certificate, Fee Structure Certificate for semester 7/8) and visually verified fonts, justification, margins, and the semester-label fix