Add bd human command for focused help menu

bd has 70+ commands, which can be overwhelming for human users who just
want to track issues. The new `bd human` command displays a curated list
of ~15 essential commands organized by workflow:

- Working With Issues: create, list, show, update, close, reopen, comment
- Finding Work: ready, search, status, stats
- Dependencies: dep add/remove/tree, graph, blocked
- Setup & Sync: init, sync, doctor
- Getting Help: quickstart, help, --help

Also includes quick examples showing common workflows.

Changes:
- Add cmd/bd/human.go with curated help output
- Add "human" to noDbCommands list in main.go (no database needed)

cmd/bd/main.go

@@ -275,6 +275,7 @@ var rootCmd = &cobra.Command{
 			"fish",
 			"help",
 			"hooks",
+			"human",
 			"init",
 			"merge",
 			"onboard",