chore: remove dead projects and legacy .sln

Delete unused/orphaned projects not referenced by the solution or any
csproj:
- cdeWeb + cdeWebTest (unreleased ASP.NET/Angular web frontend) and its
  karma/jasmine harness under src/tests
- NUnit.Should (BDD .Should() helper; no usages anywhere)
- Finder (standalone WPF experiment)
- cdeLibSpec + cdeLibSpec2 (orphaned spec/BDDfy sample projects)

Also drop src/cde.sln in favour of the maintained cde.slnx and repoint
the Fallout build (.fallout/parameters.json) at the .slnx. Remove the
stale cdeWeb section from Readme.md.

Author: jafin

.fallout/parameters.json

@@ -1,4 +1,4 @@
 {
   "$schema": "./build.schema.json",
-  "Solution": "src/cde.sln"
+  "Solution": "src/cde.slnx"
 }

Readme.md

@@ -32,12 +32,6 @@ This application reads and writes a configuration file `cdeWinView.cfg`.
 
 The executable `cdeWin.exe` can be copied around by it self to be used anywhere that .NET 10 is available with the behavior of the cdeWinView.cfg file as described just above.
 
-#### cdeWeb (unreleased)
-
-This a web interface version of cde for searching but it is not released or finished.
-
-It is built with ASP.Net, MVC, SignalR, Bootstrap and Angular.js.
-
 ### Contact Author
 
 My name is Robin and you can contact me about cde on the github repository site.