Restructure documentation navigation

 - Only the catalog is updated. No existing links are changed
 - Move 'AI Concepts' under 'Overview'
 - Reorganize API sections for better hierarchy
 - Move 'Vector Databases' into its own top-level section
 - Reposition 'Function Calling', 'Multimodality', 'Testing', and 'Structured Output' as top-level items
 - Remove redundant nesting in some sections
 - Comment out 'Generic Model' section

Author: tzolov

spring-ai-docs/src/main/antora/modules/ROOT/nav.adoc

@@ -1,9 +1,10 @@
 * xref:index.adoc[Overview]
-* xref:concepts.adoc[AI Concepts]
+** xref:concepts.adoc[AI Concepts]
 * xref:getting-started.adoc[Getting Started]
-* xref:api/index.adoc[]
-** xref:api/chatclient.adoc[]
-*** xref:api/advisors.adoc[Advisors]
+* xref:api/chatclient.adoc[]
+** xref:api/advisors.adoc[Advisors]
+* xref:api/index.adoc[AI Model API]
+** xref:api/prompt.adoc[]
 ** xref:api/chatmodel.adoc[]
 *** xref:api/bedrock-chat.adoc[Amazon Bedrock]
 **** xref:api/chat/bedrock/bedrock-anthropic3.adoc[Anthropic3]
@@ -70,35 +71,34 @@
 **** xref:api/audio/speech/openai-speech.adoc[OpenAI]
 ** xref:api/moderation[Moderation Model API]
 *** xref:api/moderation/openai-moderation.adoc[OpenAI]
+// ** xref:api/generic-model.adoc[]
 
-** xref:api/vectordbs.adoc[]
-*** xref:api/vectordbs/azure.adoc[]
-*** xref:api/vectordbs/apache-cassandra.adoc[]
-*** xref:api/vectordbs/chroma.adoc[]
-*** xref:api/vectordbs/elasticsearch.adoc[]
-*** xref:api/vectordbs/gemfire.adoc[GemFire]
-*** xref:api/vectordbs/milvus.adoc[]
-*** xref:api/vectordbs/mongodb.adoc[]
-*** xref:api/vectordbs/neo4j.adoc[]
-*** xref:api/vectordbs/opensearch.adoc[]
-*** xref:api/vectordbs/oracle.adoc[Oracle]
-*** xref:api/vectordbs/pgvector.adoc[]
-*** xref:api/vectordbs/pinecone.adoc[]
-*** xref:api/vectordbs/qdrant.adoc[]
-*** xref:api/vectordbs/redis.adoc[]
-*** xref:api/vectordbs/hana.adoc[SAP Hana]
-*** xref:api/vectordbs/typesense.adoc[]
-*** xref:api/vectordbs/weaviate.adoc[]
-
-** xref:api/functions.adoc[Function Calling]
-** xref:api/multimodality.adoc[Multimodality]
-** xref:api/prompt.adoc[]
-** xref:api/structured-output-converter.adoc[Structured Output]
+* xref:api/vectordbs.adoc[]
 ** xref:api/etl-pipeline.adoc[]
-** xref:api/testing.adoc[]
-** xref:api/generic-model.adoc[]
+** xref:api/vectordbs/azure.adoc[]
+** xref:api/vectordbs/apache-cassandra.adoc[]
+** xref:api/vectordbs/chroma.adoc[]
+** xref:api/vectordbs/elasticsearch.adoc[]
+** xref:api/vectordbs/gemfire.adoc[GemFire]
+** xref:api/vectordbs/milvus.adoc[]
+** xref:api/vectordbs/mongodb.adoc[]
+** xref:api/vectordbs/neo4j.adoc[]
+** xref:api/vectordbs/opensearch.adoc[]
+** xref:api/vectordbs/oracle.adoc[Oracle]
+** xref:api/vectordbs/pgvector.adoc[]
+** xref:api/vectordbs/pinecone.adoc[]
+** xref:api/vectordbs/qdrant.adoc[]
+** xref:api/vectordbs/redis.adoc[]
+** xref:api/vectordbs/hana.adoc[SAP Hana]
+** xref:api/vectordbs/typesense.adoc[]
+** xref:api/vectordbs/weaviate.adoc[]
+
 
 * xref:observabilty/index.adoc[]
+* xref:api/functions.adoc[Function Calling]
+* xref:api/multimodality.adoc[Multimodality]
+* xref:api/testing.adoc[]
+* xref:api/structured-output-converter.adoc[Structured Output]
 
 * Service Connections
 ** xref:api/docker-compose.adoc[Docker Compose]