Add i18n module: MessageSource, LocaleResolver and localized ProblemDetail

English, Marathi and Hindi bundles behind one small web app, with tests that run it on a real
port and write the transcripts (01-11) quoted in the article, plus a jar-metadata capture (12).

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Uu7q8vPeREyT4218EJPzz1

i18n/output/12-configuration-metadata.txt

@@ -0,0 +1,31 @@
+# spring.messages.* and spring.web.locale* in the configuration metadata shipped with Spring Boot 4.1.1
+
+jar: spring-boot-autoconfigure-4.1.1.jar
+
+spring.messages.always-use-message-format
+    type:    java.lang.Boolean
+    default: false
+spring.messages.basename
+    type:    java.util.List<java.lang.String>
+    default: ["messages"]
+spring.messages.cache-duration
+    type:    java.time.Duration
+    default: (none)
+spring.messages.common-messages
+    type:    java.util.List<org.springframework.core.io.Resource>
+    default: (none)
+spring.messages.encoding
+    type:    java.nio.charset.Charset
+    default: "UTF-8"
+spring.messages.fallback-to-system-locale
+    type:    java.lang.Boolean
+    default: true
+spring.messages.use-code-as-default-message
+    type:    java.lang.Boolean
+    default: false
+spring.web.locale
+    type:    java.util.Locale
+    default: (none)
+spring.web.locale-resolver
+    type:    org.springframework.boot.autoconfigure.web.WebProperties$LocaleResolver
+    default: "accept-header"