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/memo/plugin.json

@@ -1,8 +0,0 @@
-{
-  "name": "memo",
-  "version": "1.0.0",
-  "description": "备忘插件，支持创建、完成、列出备忘条目，自动提醒",
-  "author": "HomeAgent",
-  "entry": "plugin.so",
-  "tags": ["memo", "reminder", "todo"]
-}