refactor: Finalize agent template

sources/agents/claude_sonnet_chat.toml

@@ -1,77 +1,14 @@
 schema_version = 1
 
+extends     = "Anthropic Base Chat"
 name        = "Claude Sonnet Chat"
-description = "Anthropic Claude (Messages API) — coding chat assistant via the hosted Claude provider."
-
-provider_instance = "Claude"
-endpoint          = "/v1/messages"
+description = "Anthropic Claude Sonnet 4.6 (Messages API) — coding chat assistant with thinking."
 
 model = "claude-sonnet-4-6"
 
-role = """
-You are a helpful coding assistant integrated into Qt Creator.
-Answer concisely. When the user shares code, prefer concrete diffs or
-minimal patches over rewriting whole files. Use markdown code blocks
-with language tags so the IDE can render them.
-"""
-
 enable_thinking = true
-enable_tools    = true
-
 tags = ["chat", "claude", "anthropic", "cloud"]
 
-context = """
-{%- set readme = read_file("${PROJECT_DIR}/README.md") -%}
-{%- if length(readme) > 0 %}
-## Project README.md
-{{ readme }}
-{%- endif %}
-"""
-
-[template]
-message_format = """
-{
-  {%- if existsIn(ctx, "system_prompt") %}
-  "system": {{ tojson(ctx.system_prompt) }},
-  {%- endif %}
-  "messages": [
-    {%- for msg in ctx.history %}
-    {
-      "role": {{ tojson(msg.role) }},
-      "content": [
-        {%- for b in msg.content_blocks %}
-        {%- if b.type == "image" %}
-        {
-          "type": "image",
-          "source": {
-            {%- if b.is_url %}
-            "type": "url",
-            "url": {{ tojson(b.data) }}
-            {%- else %}
-            "type": "base64",
-            "media_type": {{ tojson(b.media_type) }},
-            "data": {{ tojson(b.data) }}
-            {%- endif %}
-          }
-        }{% if not loop.is_last %},{% endif %}
-        {%- else %}
-        {{ tojson(b) }}{% if not loop.is_last %},{% endif %}
-        {%- endif %}
-        {%- endfor %}
-      ]
-    }{% if not loop.is_last %},{% endif %}
-    {%- endfor %}
-  ]
-}
-"""
-
-[template.sampling]
-max_tokens  = 8192
-temperature = 1
-
-[template.thinking.overrides]
-temperature = 1
-
-[template.thinking.request_block.thinking]
-type          = "enabled"
-budget_tokens = 4096
+[body]
+max_tokens = 8192
+thinking   = { type = "enabled", budget_tokens = 4096 }