Feat/swift errorHandling

[nank1ro]

Summary

Adds a new Swift argument, errorHandling, with 16 exercises (order 29) across all 12 locales (en, it, de, es, fr, hi, it, ja, ko, pl, pt, ru, zh).

Exercise mix: 7 type-1 (Run Code), 4 type-2 (Fill Empty Spaces), 3 type-3 (Choose Answer), 2 type-4 (Sort Items).

Concepts, in order:

1. Declaring an Error type and handling a thrown error with do/catch (1, type 2)
2. Marking a function throws and throwing a custom error (2, type 1)
3. Catching a specific error case by name (3, type 2)
4. Reading do/catch control flow (4, type 3)
5. Errors with associated values (5, type 1)
6. Ordering error declaration → throwing function → do/catch (6, type 4)
7. guard ... else { throw } (7, type 1)
8. try? and optional results (8, type 2)
9. try? with ?? for a default value (9, type 1)
10. When try! is appropriate (10, type 3)
11. defer for cleanup on both normal return and throw (11, type 1)
12. Reading nested error propagation (12, type 3)
13. Rethrowing functions (rethrows) with throwing closures (13, type 1)
14. Catching multiple distinct error cases separately (14, type 2)
15. Ordering error declaration → function → loop with do/catch (15, type 4)
16. Capstone validator combining the chapter's concepts (16, type 1)

Checks run

• validator: pass
• tester: pass — 7 type-1 exercises (2, 5, 7, 9, 11, 13, 16), 7/7 passed against codecompiler-8081
• check_outputs_docker.sh: pass — 6 type-2/4 exercises (1, 3, 6, 8, 14, 15), 0 failed
• check_locales.py: pass — 0 problems across 17 en files x 11 locales; all 12 locales have the 16 exercises plus _theory.md, and all 12 swift/data.json files declare errorHandling
• curriculum.json and all _theory.md files regenerated

Known issues

None.