fix: cap distiller startup scan and switch to formal SDK module dependency

- replace vendored third_party/homeagent-sdk with formal module dependency
- keep canonical SDK via go.mod pinned commit
- optimize distiller startup loading to stream recent raw records only
- parse timestamps correctly and cap startup load to 5000 records
- remove quadratic string building in raw record parsing
- restore fast startup while preserving memory pipeline

third_party/homeagent-sdk/example/files/plugin.json

@@ -1,8 +0,0 @@
-{
-  "name": "files",
-  "version": "1.0.0",
-  "description": "文件系统操作插件，提供文件读写、编辑、目录列表等工具",
-  "author": "HomeAgent",
-  "entry": "plugin.so",
-  "tags": ["files", "filesystem", "io"]
-}