feat: Implement learn command for agent tool with knowledge management features

- Introduced the `agent learn` command to manage learned knowledge, including user preferences, ROM patterns, project context, and conversation memory.
- Added functionality for setting, getting, listing preferences, and managing project contexts.
- Implemented memory storage and retrieval, allowing the agent to remember past conversations and key facts.
- Enhanced CLI output with usage instructions and error handling for the learn command.
- Created a new `LearnedKnowledgeService` to handle persistent data storage and retrieval.

src/cli/handlers/agent.cc

@@ -110,7 +110,7 @@ absl::Status Agent::Run(const std::vector<std::string>& arg_vec) {
     return agent::HandleGuiCommand(subcommand_args);
   }
   if (subcommand == "learn") {
-    return agent::HandleLearnCommand();
+    return agent::HandleLearnCommand(subcommand_args);
   }
   if (subcommand == "list") {
     return agent::HandleListCommand();