fix(quizzes): align selectedIndex max in submitQuizSchema with MAX_QUIZ_OPTIONS (#538)

[lmduy2612]

Summary

Closes #538.

Aligns selectedIndex maximum boundary in submitQuizSchema (src/modules/quizzes/quiz.types.ts) with MAX_QUIZ_OPTIONS - 1, preventing out-of-range option index submissions that cause false-positive server warning logs.

Changes Made

• Moved MIN_QUIZ_OPTIONS (2) and MAX_QUIZ_OPTIONS (10) to the primary Constants section in src/modules/quizzes/quiz.types.ts.
• Updated submitQuizSchema to bound selectedIndex using max(MAX_QUIZ_OPTIONS - 1) instead of the static max(20).
• Updated tests/unit/schemas/input-validation.test.ts to verify that valid option indices (0 through MAX_QUIZ_OPTIONS - 1) are accepted, while indices at or above MAX_QUIZ_OPTIONS are rejected by the schema.
• Verified all schema and quiz validation tests pass 100% (34/34 tests green).

Acceptance Criteria

• Align selectedIndex max with MAX_QUIZ_OPTIONS (10 options -> index 0-9)
• Reduce false-positive warnings in logs for out-of-range option indices