test: add full test coverage for notes, ues, ue-modules, ajustements, enseignements, users

- Unit tests (mock DB + API) for all missing endpoints
- Integration tests (Drizzle direct) for all missing entities
- E2E tests (handler + real DB) for all missing endpoints
- Robustness tests: invalid inputs, SQL injection, type errors, business rule violations
- Seed helpers: seedNotes, seedUeModules, seedEnseignements, seedAjustements
- Add test:coverage and test:coverage:html tasks to deno.json

Tests expose known handler bugs (marked [BUG] in test names):
- ajustements PUT/DELETE: .where() without and() modifies all rows for student
- Missing try/catch in modules, users, enseignements handlers
- Whitespace accepted as valid string values
- No type or business rule validation (note bounds, coeff >= 0)

deno.json

@@ -14,6 +14,8 @@
     "test:unit": "deno test -A --no-check tests/unit/",
     "test:integration": "deno test -A --no-check tests/integration/",
     "test:e2e": "deno test -A --no-check tests/e2e/",
+    "test:coverage": "deno test -A --no-check --coverage=coverage tests/ && deno coverage coverage --exclude=tests/",
+    "test:coverage:html": "deno test -A --no-check --coverage=coverage tests/ && deno coverage coverage --exclude=tests/ --html",
     "migrate": "node_modules/.bin/drizzle-kit migrate"
   },
   "lint": {