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

AGENTS.md

@@ -26,6 +26,16 @@ agent/sandbox shells, and SDK 10 additionally fails without
 scripts/dotnet.sh build db-subclass-to-dto.sln
 scripts/dotnet.sh test db-subclass-to-dto.sln
 scripts/run-tests.sh          # full test suite, from repo root
+scripts/run-console.sh        # run the Before.Console demo (bash; delegates
+                              # to dotnet.sh); app args go after `--`
+```
+
+Windows/PowerShell counterpart:
+
+```powershell
+scripts\run-console.ps1       # run the Before.Console demo; app args go
+                              # directly (the script inserts `--` for
+                              # dotnet run); needs no DOTNET_CLI_HOME setup
 ```
 
 The wrappers cd to the repo root (the test runner must run from the parent