feat: add bd tree to Key Commands in gt prime output

- Add `bd tree <id>` to Key Commands in bd prime template (beads.go)
- Add `bd tree <issue>` to prime_output.go for mayor/polecat/crew roles
- Helps agents understand bead ancestry, siblings, and dependencies

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/beads/beads.go

@@ -747,6 +747,8 @@ This is physics, not politeness. Gas Town is a steam engine - you are a piston.
 - ` + "`gt mol status`" + ` - Check your hooked work
 - ` + "`gt mail inbox`" + ` - Check for messages
 - ` + "`bd ready`" + ` - Find available work (no blockers)
+- ` + "`bd tree <id>`" + ` - View bead ancestry, siblings, and dependencies
+- ` + "`bd sync`" + ` - Sync beads changes
 
 ## Session Close Protocol