feat(backend): implement step 4 — EmailContext and EmailReaderService

backend/src/main/kotlin/com/condado/newsletter/model/EmailContext.kt

@@ -0,0 +1,14 @@
+package com.condado.newsletter.model
+
+import java.time.LocalDateTime
+
+/**
+ * A snapshot of a single email read from the shared company IMAP inbox.
+ * Used as context when building the AI prompt.
+ */
+data class EmailContext(
+    val from: String,
+    val subject: String,
+    val body: String,
+    val receivedAt: LocalDateTime
+)