fix(exam): stop Create/Update Exam form from silently failing to submit

Three bugs compounded into a button that looked unwired:

- cuttingPoint carried a native HTML required attribute while sitting on
  the hidden Settings tab (Mantine keeps inactive tab panels mounted with
  display:none). The browser blocked form submission entirely, silently
  - no toast, no error, nothing. Replaced required with withAsterisk and
  moved validation into JS.
- Manual required-field validation never checked type/form/adminMethod/
  evalMethod/cuttingPoint at all, so even without the native block above
  a half-filled Settings tab would silently no-op. Validation now covers
  every required field on both tabs and switches to whichever tab has
  the problem.
- Filling only the English Direction field (leaving Amharic blank) passed
  frontend validation but the backend hard-rejects it, producing a 400
  with a confusing error. Frontend now requires both-or-neither, matching
  the same rule already applied to MCQ options.

Also translates the previously hardcoded validation message in both
locales.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/backoffice/src/app/i18n/locales/am.ts

@@ -254,6 +254,9 @@ export const am: Translations = {
       random: "በዘፈቀደ",
       cuttingPoint: "የማለፊያ ነጥብ",
       cuttingPointPlaceholder: "ለማለፍ ዝቅተኛ ነጥብ",
+      fillRequiredBasic: "በመሠረታዊ መረጃ ውስጥ ያሉ አስፈላጊ መስኮችን ይሙሉ።",
+      fillRequiredSettings: "በቅንብሮች ውስጥ ያሉ አስፈላጊ መስኮችን ይሙሉ — ዓይነት፣ ቅጽ፣ የአስተዳደር ዘዴ፣ የግምገማ ዘዴ እና የማለፊያ ነጥብ።",
+      directionBothLanguages: "መመሪያ በሁለቱም እንግሊዝኛ እና አማርኛ ጽሑፍ ያስፈልገዋል፣ ወይም ሁለቱንም ባዶ ይተዉ።",
       status: "ሁኔታ",
       statusPlaceholder: "የፈተና ሁኔታ",
       pending: "በመጠባበቅ ላይ",

apps/backoffice/src/app/i18n/locales/en.ts

@@ -251,6 +251,9 @@ export const en = {
       random: 'Random',
       cuttingPoint: 'Cutting Point (Pass Mark)',
       cuttingPointPlaceholder: 'Minimum score to pass',
+      fillRequiredBasic: 'Please fill all required fields in Basic Info.',
+      fillRequiredSettings: 'Please fill all required fields in Settings — type, form, administration method, evaluation method, and cutting point.',
+      directionBothLanguages: 'Direction needs text in both English and Amharic, or leave both empty.',
       status: 'Status',
       statusPlaceholder: 'Exam status',
       pending: 'Pending',