feat: render GGUF Jinja template via minijinja crate

- Replaced manual prompt building with GGUF's chat template rendered through minijinja (Rust Jinja2 engine)
- Simplified template: removed multi-step tool detection, reasoning extraction (not needed at template level)
- Added reasoning_content separation: clean_text() returns (reasoning, answer) tuple
- Added reasoning_content field to ResponseMessage and SseDelta for OpenAI-compatible output
- Embedded template at build time via include_str! from templates/chat_template.jinja
- Built-in support for enable_thinking, tool_definitions, tool_calls, tool_response

src/domain/entity/mod.rs

@@ -96,8 +96,11 @@ pub struct Choice {
 #[derive(Serialize)]
 pub struct ResponseMessage {
     pub role: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub content: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
+    pub reasoning_content: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub tool_calls: Option<Vec<ToolCall>>,
 }
 
@@ -165,6 +168,8 @@ pub struct SseDelta {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub content: Option<String>,
     #[serde(skip_serializing_if = "Option::is_none")]
+    pub reasoning_content: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub tool_calls: Option<Vec<ToolCall>>,
 }