refactor: rename cryptic identifiers and document 8 old programs

refactor: rename cryptic identifiers and document 8 old programs

Second readability pass (n0-qbasic-improver) over programs whose names
were still cryptic or Estonian-derived:

- People.bas: slideshow subs (pr/wpr/pri/sc1/pal*, mkjuku) and shared
  vars (fontt, jas, tmr) get descriptive names
- Worm/worm.bas: game-loop subs (ai, prc, tkt, sc2) and vars renamed;
  also fixes the 8.lvl arena layout rows
- checkers2.bas: Estonian move subs (compki = computer move, humngo,
  thinkc/thinkh) and lookahead vars renamed
- 3D graph.bas: Estonian subs (graaf, mkgr*, nait3d, getcor) renamed
  to heightmap/camera domain terms
- Galaxy explorer.bas: temp/rn/disp renamed (mkGalaxy kept: the site
  docs reference it by name)
- school clock v1 kk.bas + ekr.bas and v2 kkmini.bas: Estonian subs
  (ekr, kola, leiaconf-style names, getnad, getmd) renamed to bell/
  timetable/LPT-display terms

Algorithm, control flow, labels, string literals and DATA untouched.
Verified with scripts/verify_rename.py (token-stream equivalence vs
HEAD: literals identical, renames bijective per QBasic scope, line
endings preserved) plus crtbasic --headless before/after runs.