Add new action skills for AL testing and documentation

- Introduced `al-test-writer` to generate AL test codeunits for production objects based on TDD principles.
- Added `al-userguide-test-writer` to create test codeunits from user guide steps, mapping actions and assertions.
- Implemented `bc-extension-test-guide` to generate a comprehensive TEST_GUIDE.md for Business Central extensions, covering various categories.
- Created `bc-webclient-runner` to automate UI testing of the Business Central web client, capturing screenshots and asserting UI states.
- Developed `page-scripting-e2e` to produce a recording plan for Page Scripting, ensuring a structured approach to browser-level testing.

custom/knowledge/integration/send-an-idempotency-key-on-every-outbound-call.good.al

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+// Best practice: every outbound call carries Idempotency-Key = the Integration Message GUID.
+// The key is created once when the message is staged and never changes, so the first call
+// and every retry (Job Queue or operator-driven) send the SAME key. A well-behaved receiver
+// collapses them into a single side effect and returns the original response.
+
+codeunit 50150 "Outbound Caller"
+{
+    procedure Send(var IntegrationMessage: Record "Integration Message")
+    var
+        Client: HttpClient;
+        Request: HttpRequestMessage;
+        Content: HttpContent;
+        ContentHeaders: HttpHeaders;
+        RequestHeaders: HttpHeaders;
+        Response: HttpResponseMessage;
+    begin
+        Content.WriteFrom(IntegrationMessage.GetRequest());
+
+        // Content-Type belongs on the content headers, not the request headers.
+        Content.GetHeaders(ContentHeaders);
+        if ContentHeaders.Contains('Content-Type') then
+            ContentHeaders.Remove('Content-Type');
+        ContentHeaders.Add('Content-Type', 'application/json');
+
+        Request.Content := Content;
+        Request.Method := 'POST';
+        Request.SetRequestUri('https://pay.contoso.com/api/charges');
+        Request.GetHeaders(RequestHeaders);
+
+        // THE key line. The value is the staged Message ID, which is stable for the life of
+        // the message. Calling Send again for the same row sends this exact same value, so the
+        // payment service sees the retry as a repeat of one charge and captures money once.
+        RequestHeaders.Add('Idempotency-Key', StableKey(IntegrationMessage));
+
+        // After an UNCERTAIN failure (timeout, dropped connection, 502) the Job Queue will
+        // re-run this message. Because the key is unchanged, the retry is safe: no double charge.
+        Client.Send(Request, Response);
+        IntegrationMessage.RecordResult(Response);
+    end;
+
+    // The key is derived purely from the durable message id. Nothing here changes between
+    // attempts: no CreateGuid, no timestamp, no attempt counter.
+    local procedure StableKey(IntegrationMessage: Record "Integration Message"): Text
+    begin
+        exit(DelChr(LowerCase(Format(IntegrationMessage."Message ID")), '=', '{}'));
+    end;
+}