feat: converge dynamic plugins onto canonical homeagent-sdk

- Separate built-in plugin interface from external plugin interface
- Route dynamic plugin loading through homeagent-sdk/sdk using reflection
- Turn internal/sdk into an enhanced wrapper over canonical SDK types
- Vendor SDK repo snapshot under third_party/homeagent-sdk for stable builds
- Keep internal constructors/adapters for memory, knowledge, llm, settings
- Align dynamic QQ loading with canonical SDK chain

third_party/homeagent-sdk/hack/plugin-dev/templates/Makefile.tmpl

@@ -0,0 +1,17 @@
+# Build external Go plugin for HomeAgent
+# Usage: make          # build plugin.so
+#        make clean    # remove plugin.so
+
+PLUGIN_DIR := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
+SDK_ROOT := $(realpath $(PLUGIN_DIR)../..)
+PLUGIN_NAME := $(notdir $(realpath $(PLUGIN_DIR)))
+
+.PHONY: all clean
+
+all: plugin.so
+
+plugin.so:
+	cd $(SDK_ROOT) && go build -buildmode=plugin -o $(PLUGIN_DIR)plugin.so $(PLUGIN_DIR)
+
+clean:
+	rm -f $(PLUGIN_DIR)plugin.so