Migrate AI Hint feed generation

Bring dynamic hint generation into the account service while preserving the legacy key.osglab.com deployment for existing clients.

src/main/kotlin/com/osglab/account/config/AppConfig.kt

@@ -3,6 +3,7 @@ package com.osglab.account.config
 import com.osglab.account.features.storekit.domain.StoreKitProduct
 import io.ktor.server.config.ApplicationConfig
 import java.net.URI
+import java.time.ZoneId
 import java.util.Base64
 import java.util.UUID
 
@@ -21,6 +22,7 @@ data class AppConfig(
     val providers: ProvidersConfig,
     val integrity: IntegrityConfig,
     val admin: AdminConfig = AdminConfig(),
+    val hintFeed: HintFeedConfig = HintFeedConfig(),
 ) {
     val isProduction: Boolean = environment == Environment.PRODUCTION
 
@@ -187,6 +189,18 @@ data class AppConfig(
                     100_000,
                 ),
             )
+            val hintFeed = HintFeedConfig(
+                enabled = config.booleanOrDefault("app.hintFeed.enabled", false),
+                topHubApiKey = config.optionalSecret(
+                    "app.hintFeed.topHubApiKey",
+                    production = false,
+                ),
+                zoneId = config.valueOrDefault("app.hintFeed.zoneId", "UTC").let { raw ->
+                    runCatching { ZoneId.of(raw) }.getOrElse { cause ->
+                        throw ConfigValidationException("app.hintFeed.zoneId must be a valid time zone", cause)
+                    }
+                },
+            )
 
             require(session.hmacSecret.size >= MIN_HMAC_SECRET_BYTES) {
                 "app.session.secret must contain at least $MIN_HMAC_SECRET_BYTES bytes"
@@ -329,6 +343,7 @@ data class AppConfig(
                 providers = providers,
                 integrity = integrity,
                 admin = admin,
+                hintFeed = hintFeed,
             )
         }
     }
@@ -371,6 +386,12 @@ data class AntiAbuseConfig(
     val tombstoneRetentionDays: Long,
 )
 
+data class HintFeedConfig(
+    val enabled: Boolean = false,
+    val topHubApiKey: String? = null,
+    val zoneId: ZoneId = ZoneId.of("UTC"),
+)
+
 data class AppleConfig(
     val teamId: String?,
     val keyId: String?,