Throw ObjectNotFoundException from FindRequired; add run-console wrappers

- DbBase.FindRequired / Client.FindByNameRequired now throw the
  domain-specific ObjectNotFoundException (NHibernate lineage; Rails
  equivalent: ActiveRecord::RecordNotFound) on a lookup miss; the
  no-context case stays InvalidOperationException (configuration error)
- Console demo catches the new type; tests (18)/(21) assert it,
  (19)/(23) keep InvalidOperationException with rationale comments
- scripts/run-console.sh delegates to dotnet.sh; run-console.ps1 is
  the Windows/PowerShell counterpart (mise-first, repo-root cd)

Yak: objectnotfoundexception-run-console-wrappers-3p8b

src/Before/DbBase.cs

@@ -86,8 +86,9 @@ public class DbBase
     /// <summary>
     /// Throwing variant of <see cref="Find{T}(System.Predicate{T},DbContext?)"/>.  Finds the first entity
     /// whose runtime type matches <typeparamref name="T"/> and satisfies
-    /// <paramref name="predicate"/>.  Throws <see cref="InvalidOperationException"/>
-    /// when no match is found or when no <see cref="Context"/> singleton is configured.
+    /// <paramref name="predicate"/>.  Throws <see cref="ObjectNotFoundException"/>
+    /// when no match is found, and <see cref="InvalidOperationException"/> when no
+    /// <see cref="Context"/> singleton is configured (a configuration error, not a lookup miss).
     ///
     /// The exception message includes <paramref name="predicateToString"/> so
     /// callers can debug which lookup failed.
@@ -98,8 +99,11 @@ public class DbBase
     /// <param name="predicateToString">A human-readable description of the predicate, used in the
     /// exception message when the search fails.</param>
     /// <returns>The first matching entity.</returns>
+    /// <exception cref="ObjectNotFoundException">
+    /// Thrown when no entity matches <paramref name="predicate"/>.
+    /// </exception>
     /// <exception cref="InvalidOperationException">
-    /// Thrown when no entity matches <paramref name="predicate"/> or when no context is available.
+    /// Thrown when no context is available (neither passed explicitly nor set as the singleton).
     /// </exception>
     public static T FindRequired<T>(Predicate<T> predicate, DbContext? db, string predicateToString)
         where T : DbBase
@@ -117,7 +121,7 @@ public class DbBase
             if (e is T candidate && predicate(candidate))
                 return candidate;
 
-        throw new InvalidOperationException(
+        throw new ObjectNotFoundException(
             $"FindRequired<{typeof(T).Name}>({predicateToString}) — " +
             $"no matching {typeof(T).Name} found in context.");
     }