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/interfaces.go

@@ -0,0 +1,27 @@
+package command
+
+import "context"
+
+// Skill represents a single skill loaded from a bot's container.
+type Skill struct {
+	Name        string
+	Description string
+}
+
+// SkillLoader loads skills for a bot.
+type SkillLoader interface {
+	LoadSkills(ctx context.Context, botID string) ([]Skill, error)
+}
+
+// FSEntry represents a file or directory in a container filesystem.
+type FSEntry struct {
+	Name  string
+	IsDir bool
+	Size  int64
+}
+
+// ContainerFS provides read-only access to a bot's container filesystem.
+type ContainerFS interface {
+	ListDir(ctx context.Context, botID, path string) ([]FSEntry, error)
+	ReadFile(ctx context.Context, botID, path string) (string, error)
+}