feat(command): extend slash command system with new commands and UX improvements

Add 9 new command groups (/model, /memory, /search, /browser, /usage,
/email, /heartbeat, /skill, /fs) and improve existing commands by hiding
internal UUIDs, resolving IDs to human-readable names in /settings, and
switching /schedule to name-based references.

internal/command/fs.go

@@ -0,0 +1,62 @@
+package command
+
+import (
+	"fmt"
+	"strings"
+)
+
+func (h *Handler) buildFSGroup() *CommandGroup {
+	g := newCommandGroup("fs", "Browse container filesystem")
+	g.Register(SubCommand{
+		Name:  "list",
+		Usage: "list [path] - List files in the container",
+		Handler: func(cc CommandContext) (string, error) {
+			if h.containerFS == nil {
+				return "Container filesystem is not available.", nil
+			}
+			dir := "/"
+			if len(cc.Args) > 0 {
+				dir = cc.Args[0]
+			}
+			entries, err := h.containerFS.ListDir(cc.Ctx, cc.BotID, dir)
+			if err != nil {
+				return "", err
+			}
+			if len(entries) == 0 {
+				return fmt.Sprintf("Directory %q is empty.", dir), nil
+			}
+			var b strings.Builder
+			fmt.Fprintf(&b, "%s:\n", dir)
+			for _, e := range entries {
+				if e.IsDir {
+					fmt.Fprintf(&b, "  %s/\n", e.Name)
+				} else {
+					fmt.Fprintf(&b, "  %s (%d bytes)\n", e.Name, e.Size)
+				}
+			}
+			return b.String(), nil
+		},
+	})
+	g.Register(SubCommand{
+		Name:  "read",
+		Usage: "read <path> - Read a file from the container",
+		Handler: func(cc CommandContext) (string, error) {
+			if h.containerFS == nil {
+				return "Container filesystem is not available.", nil
+			}
+			if len(cc.Args) < 1 {
+				return "Usage: /fs read <path>", nil
+			}
+			content, err := h.containerFS.ReadFile(cc.Ctx, cc.BotID, cc.Args[0])
+			if err != nil {
+				return "", err
+			}
+			const maxLen = 2000
+			if len(content) > maxLen {
+				content = content[:maxLen] + "\n... (truncated)"
+			}
+			return fmt.Sprintf("```\n%s\n```", content), nil
+		},
+	})
+	return g
+}