test(ego-lint): add count-based assertion for prototype-override dedup

The existing assertions only checked presence of warnings via grep -qE,
which would pass whether dedup produced 2 or 4 warnings. Add
assert_output_count helper and use it to verify exactly 2 warnings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ZviBaratz

tests/assertions/proto-override-dedup.sh

@@ -5,4 +5,5 @@ echo "=== proto-override-dedup ==="
 run_lint "proto-override-dedup@test"
 assert_output_contains "prototype override detected" "\[WARN\].*lifecycle/prototype-override.*BackgroundMenu.prototype.open"
 assert_output_contains "search prototype override detected" "\[WARN\].*lifecycle/prototype-override.*SearchController.prototype.startSearch"
+assert_output_count "exactly 2 prototype-override warnings (dedup works)" "\[WARN\].*lifecycle/prototype-override" 2
 echo ""

tests/run-tests.sh

@@ -45,6 +45,19 @@ assert_exit_code() {
     fi
 }
 
+assert_output_count() {
+    local label="$1" pattern="$2" expected="$3"
+    local actual
+    actual=$(echo "$output" | grep -cE "$pattern" || true)
+    if [[ "$actual" -eq "$expected" ]]; then
+        echo -e "  ${GREEN}✓${NC} $label (count: $actual)"
+        PASS_COUNT=$((PASS_COUNT + 1))
+    else
+        echo -e "  ${RED}✗${NC} $label (expected $expected matches, got $actual)"
+        FAIL_COUNT=$((FAIL_COUNT + 1))
+    fi
+}
+
 run_lint() {
     local fixture="$1"
     output=""