sdk: embed non-toolchain SDK in third_party, add NoMemory/Cleaner support

- Embed sdk/, example/, meta/, go.mod from homeagent-sdk (no .git)
- Core .gitignore excludes SDK toolchain: bin/, tools/, package/
- RegisterInputChannel + ChannelDef(NoMemory, Cleaner) in SDK
- IOManager input channel registry with GetInputChannelDef
- eventloop: apply channel Cleaner/NoMemory to interrupt text
- context engine: channelDefLookup applied in textForVector
- document store: ChannelCleaner param for archive functions
- All callers/adapters updated with ChannelDef{} default

third_party/homeagent-sdk/sdk/knowledge.go

@@ -0,0 +1,14 @@
+package sdk
+
+// KnowledgeAPI provides access to the knowledge store.
+type KnowledgeAPI interface {
+	Search(query string, topK int) ([]*Knowledge, error)
+	Add(name, content string) error
+	List() ([]string, error)
+}
+
+// Knowledge represents a knowledge entry.
+type Knowledge struct {
+	Name    string `json:"name"`
+	Content string `json:"content"`
+}