fix(command): add missing command handler wiring and lint fixes

Wire SetCommandHandler into ChannelInboundProcessor so slash commands
are intercepted before reaching the LLM. Also apply lint fixes across
command package (strconv.Itoa, comment formatting, unused code removal)
and remove obsolete tool-call-browser.vue component.

internal/command/email_cmd.go

@@ -1,7 +1,6 @@
 package command
 
 import (
-	"fmt"
 	"strings"
 )
 
@@ -91,5 +90,5 @@ func buildPermString(read, write, del bool) string {
 	if len(parts) == 0 {
 		return "none"
 	}
-	return fmt.Sprintf("%s", strings.Join(parts, ", "))
+	return strings.Join(parts, ", ")
 }