fix: 4 pre-release bug fixes — identity override, model config, agent sync, auto-identity

P1: identity.rs get_identity() returns empty soul/instructions for agents
without explicit identity files. This prevents the default ZCLAW personality
from overriding agent_config.system_prompt. New get_identity_or_default()
method added for the DEFAULT agent.

P2: messaging.rs now uses agent_config.model.model when available, falling
back to global Kernel config. This allows per-agent model selection.

P2: agentStore.ts loadClones retries up to 3 times (300ms interval) when
getClient() returns null, handling the coordinator initialization race.

P2: agent_create Tauri command auto-populates identity files (soul +
instructions) from creation parameters, ensuring build_system_prompt()
has content for new agents.

Also fixes conversationStore upsertActiveConversation to persist generated
conversation IDs, preventing duplicate entries on new conversations.

crates/zclaw-kernel/src/kernel/messaging.rs

@@ -41,9 +41,12 @@ impl Kernel {
         // Create or get session
         let session_id = self.memory.create_session(agent_id).await?;
 
-        // Always use Kernel's current model configuration
-        // This ensures user's "模型与 API" settings are respected
-        let model = self.config.model().to_string();
+        // Use agent-level model if configured, otherwise fall back to global config
+        let model = if !agent_config.model.model.is_empty() {
+            agent_config.model.model.clone()
+        } else {
+            self.config.model().to_string()
+        };
 
         // Create agent loop with model configuration
         let subagent_enabled = chat_mode.as_ref().and_then(|m| m.subagent_enabled).unwrap_or(false);
@@ -147,9 +150,12 @@ impl Kernel {
             None => self.memory.create_session(agent_id).await?,
         };
 
-        // Always use Kernel's current model configuration
-        // This ensures user's "模型与 API" settings are respected
-        let model = self.config.model().to_string();
+        // Use agent-level model if configured, otherwise fall back to global config
+        let model = if !agent_config.model.model.is_empty() {
+            agent_config.model.model.clone()
+        } else {
+            self.config.model().to_string()
+        };
 
         // Create agent loop with model configuration
         let subagent_enabled = chat_mode.as_ref().and_then(|m| m.subagent_enabled).unwrap_or(false);