feat(web): add vanilla JS/CSS SPA with embed.FS

Stream view with date grouping, card view sorted by usage, capture
bar with client-side grammar parsing, tag rail filter, detail pane
with card affordances (template slot fill, checklist toggle, link
open), promote modal with auto-detect, keyboard shortcuts (j/k/n/p/
Enter/dd/1/2). Dark theme, responsive layout. Embedded in Go binary.

cmd/serve.go

@@ -3,6 +3,7 @@ package cmd
 import (
 	"context"
 	"fmt"
+	"io/fs"
 	"net/http"
 	"os"
 	"os/signal"
@@ -14,6 +15,8 @@ import (
 	"github.com/spf13/cobra"
 )
 
+var WebFS fs.FS
+
 var (
 	servePort int
 	serveDev  bool
@@ -51,7 +54,10 @@ func runServe(_ *cobra.Command, _ []string) error {
 	}
 	defer store.Close()
 
-	router := api.NewRouter(store, serveDev)
+	var router = api.NewRouter(store, serveDev)
+	if WebFS != nil {
+		router = api.NewRouter(store, serveDev, WebFS)
+	}
 
 	addr := fmt.Sprintf(":%d", port)
 	srv := &http.Server{