feat(backfill): implement backfill tool for generating missing embeddings

internal/mcpserver/server.go

@@ -24,6 +24,7 @@ type ToolSet struct {
 	Recall    *tools.RecallTool
 	Summarize *tools.SummarizeTool
 	Links     *tools.LinksTool
+	Backfill  *tools.BackfillTool
 }
 
 func New(cfg config.MCPConfig, toolSet ToolSet) http.Handler {
@@ -117,6 +118,11 @@ func New(cfg config.MCPConfig, toolSet ToolSet) http.Handler {
 		Description: "Retrieve explicit links and semantic neighbors for a thought.",
 	}, toolSet.Links.Related)
 
+	addTool(server, &mcp.Tool{
+		Name:        "backfill_embeddings",
+		Description: "Generate missing embeddings for stored thoughts using the active embedding model.",
+	}, toolSet.Backfill.Handle)
+
 	return mcp.NewStreamableHTTPHandler(func(*http.Request) *mcp.Server {
 		return server
 	}, &mcp.StreamableHTTPOptions{