Add the three missing errorHandling exercise descriptions

[nank1ro]

en/kotlin/errorHandling/14.md, en/swift/errorHandling/15.md and en/swift/errorHandling/16.md shipped without a # --description--, while every other exercise in those two chapters has one — dart/errorHandling carries all 16. Before #322 that gap also truncated the generated _theory.md; #322 fixed the truncation and left the content hole visible.

Each new description says something the chapter had not said yet:

• kotlin 14 — a Result is an ordinary value, so it can be stored in a val and questioned repeatedly. A try/catch outcome is handled once, where it happened, and is then gone.
• swift 15 — where the do block sits decides the cost of one failure: inside the loop, one bad item is skipped; outside it, the loop gives up.
• swift 16 — chapter closer on who deals with the failure. No new syntax; it names the split between the function that detects a problem and the caller that decides what to do about it.

Translated into all 11 non-en locales (33 files). Fenced code and inline API names are byte-identical to English everywhere.

Diff shape

• 36 exercise files, insert-only.
• 24 _theory.md files, +420 / −0 — exactly the lines added to the exercises.
• curriculum.json, +24/−24: only trainUntil, which counts exercises that have a description (json_creator.dart:134). kotlin errorHandling 15 → 16 and swift 14 → 16, in each of the 12 locales.

Checks

• theory_creator + json_creator regenerated.
• validator: +275436: All tests passed!

Still open, not in this PR

en/python/errorHandling/14.md has the same gap. It is a multiple-choice quiz on the exception table that exercise 13 already prints in full, so there is nothing to say there that 13 does not already say. Left alone deliberately.