fix(growth,skills,kernel): Phase 0 地基修复 — 经验积累覆盖 + Skill 工具调用

Bug 1: ExperienceStore store_experience() 相同 pain_pattern 因确定性 URI
直接覆盖，新 Experience reuse_count=0 重置已有积累。修复为先检查 URI
是否已存在，若存在则合并（保留原 id/created_at，reuse_count+1）。

Bug 2: PromptOnlySkill::execute() 只做纯文本 complete()，75 个 Skill
的 tools 字段是装饰性的。修复为扩展 LlmCompleter 支持 complete_with_tools，
SkillContext 新增 tool_definitions，KernelSkillExecutor 从 ToolRegistry
解析 manifest 声明的工具定义传入 LLM function calling。

crates/zclaw-skills/src/skill.rs

@@ -3,7 +3,7 @@
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 use std::pin::Pin;
-use zclaw_types::{SkillId, Result};
+use zclaw_types::{SkillId, ToolDefinition, Result};
 
 /// Type-erased LLM completion interface.
 ///
@@ -15,6 +15,43 @@ pub trait LlmCompleter: Send + Sync {
         &self,
         prompt: &str,
     ) -> Pin<Box<dyn std::future::Future<Output = std::result::Result<String, String>> + Send + '_>>;
+
+    /// Complete a prompt with tool definitions available to the LLM.
+    ///
+    /// The LLM may return text, tool calls, or both. Tool calls are returned
+    /// in the `tool_calls` field for the caller to execute or relay.
+    /// Default implementation falls back to plain `complete()`.
+    fn complete_with_tools(
+        &self,
+        prompt: &str,
+        _system_prompt: Option<&str>,
+        _tools: Vec<ToolDefinition>,
+    ) -> Pin<Box<dyn std::future::Future<Output = std::result::Result<SkillCompletion, String>> + Send + '_>> {
+        let prompt = prompt.to_string();
+        Box::pin(async move {
+            self.complete(&prompt).await.map(|text| SkillCompletion { text, tool_calls: vec![] })
+        })
+    }
+}
+
+/// Result of an LLM completion that may include tool calls.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SkillCompletion {
+    /// The text portion of the LLM response.
+    pub text: String,
+    /// Tool calls the LLM requested, if any.
+    pub tool_calls: Vec<SkillToolCall>,
+}
+
+/// A single tool call returned by the LLM during skill execution.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SkillToolCall {
+    /// Unique call ID.
+    pub id: String,
+    /// Name of the tool to invoke.
+    pub name: String,
+    /// Input arguments for the tool.
+    pub input: Value,
 }
 
 /// Skill manifest definition
@@ -97,6 +134,9 @@ pub struct SkillContext {
     pub file_access_allowed: bool,
     /// Optional LLM completer for skills that need AI generation (e.g. PromptOnly)
     pub llm: Option<std::sync::Arc<dyn LlmCompleter>>,
+    /// Tool definitions resolved from the skill manifest's `tools` field.
+    /// Populated by the kernel when creating the context.
+    pub tool_definitions: Vec<ToolDefinition>,
 }
 
 impl std::fmt::Debug for SkillContext {
@@ -109,6 +149,7 @@ impl std::fmt::Debug for SkillContext {
             .field("network_allowed", &self.network_allowed)
             .field("file_access_allowed", &self.file_access_allowed)
             .field("llm", &self.llm.as_ref().map(|_| "Arc<dyn LlmCompleter>"))
+            .field("tool_definitions", &self.tool_definitions.len())
             .finish()
     }
 }
@@ -124,6 +165,7 @@ impl Default for SkillContext {
             network_allowed: false,
             file_access_allowed: false,
             llm: None,
+            tool_definitions: Vec::new(),
         }
     }
 }