docs: add Javadoc to config store interfaces (batch 2 of 2)

[ginccc]

Summary

Continuation of interface Javadoc coverage for the configs package.

Interfaces to document (8)

• src/main/java/ai/labs/eddi/configs/channels/IChannelIntegrationStore.java
• src/main/java/ai/labs/eddi/configs/deployment/IDeploymentStore.java
• src/main/java/ai/labs/eddi/configs/descriptors/IDocumentDescriptorStore.java
• src/main/java/ai/labs/eddi/configs/propertysetter/IPropertySetterStore.java
• src/main/java/ai/labs/eddi/configs/snippets/IPromptSnippetStore.java
• src/main/java/ai/labs/eddi/configs/rag/IRagStore.java
• src/main/java/ai/labs/eddi/configs/properties/IUserMemoryStore.java
• src/main/java/ai/labs/eddi/configs/groups/IAgentGroupStore.java

How to write good Javadoc

1. Read the implementation class to understand what the interface does
2. Look at the model class it operates on
3. Write 2-3 lines: purpose + what consumes it + key behaviors

Good example (see IConversationMemoryStore):

/**
 * Persistence store for conversation memory snapshots.
 * Called by the lifecycle pipeline to save/load conversation state
 * between turns and across server restarts.
 */

Bad example (don't do this):

/** Store for agents. */

Note: If the interface currently has only /** @author ginccc */, replace it with
meaningful Javadoc. Per CONTRIBUTING.md, @author tags are not used in new code.

Acceptance criteria

• All 8 interfaces have class-level Javadoc (2+ meaningful lines)
• Any existing @author tags are removed
• ./mvnw compile passes