Add getting-started module: ChatClient fluent API, system/user prompts, streaming, and provider switching via spring.ai.model.chat

getting-started/output/05-real-network-round-trip.txt

@@ -0,0 +1,26 @@
+# A real HTTP round trip to OpenAI (not scripted) -- captured manually, not by run-all.sh
+
+This one is not reproducible by scripts/run-all.sh: it needs a live network path to
+api.openai.com, which the automated test suite deliberately does not depend on (see
+ChatClientEndpointsTest, which uses FakeChatModel instead). It is included because it is the
+one exhibit in this module that touches a real provider, and it proves the request pipeline
+-- ChatClient, the OpenAiChatModel bean spring.ai.model.chat=openai selected, and the OpenAI
+Java SDK underneath it -- is wired correctly all the way to OpenAI's own server, not just to
+a stub.
+
+Command (full application, spring-boot:run, a syntactically valid but fake key):
+
+  $ export OPENAI_API_KEY=sk-test-placeholder-not-a-real-key
+  $ curl 'http://localhost:8080/api/chat?message=hi'
+
+Response: HTTP 500, body in 05-real-openai-401-response-body.txt
+
+Application log root cause (grepped from the running process's stdout):
+
+  com.openai.errors.UnauthorizedException: 401: Incorrect API key provided: sk-test-**********************-key. You can find your API key at https://platform.openai.com/account/api-keys.
+
+That 401 comes from OpenAI's own server, not from Spring AI or from this sandbox -- OpenAI
+validated the key format, rejected it, and said so in its own error class
+(com.openai.errors.UnauthorizedException). A malformed request, a wrong base URL, or a client
+that never left the JVM would not look like this. Swap in a real key and this becomes a real
+reply.