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 +747,7 @@ 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

internal/cmd/prime_output.go

@@ -113,6 +113,7 @@ func outputMayorContext(ctx RoleContext) {
 	fmt.Println("- `gt status` - Show overall town status")
 	fmt.Println("- `gt rig list` - List all rigs")
 	fmt.Println("- `bd ready` - Issues ready to work")
+	fmt.Println("- `bd tree <issue>` - View ancestry, siblings, dependencies")
 	fmt.Println()
 	fmt.Println("## Hookable Mail")
 	fmt.Println("Mail can be hooked for ad-hoc instructions: `gt hook attach <mail-id>`")
@@ -176,6 +177,7 @@ func outputPolecatContext(ctx RoleContext) {
 	fmt.Println("## Key Commands")
 	fmt.Println("- `gt mail inbox` - Check your inbox for work assignments")
 	fmt.Println("- `bd show <issue>` - View your assigned issue")
+	fmt.Println("- `bd tree <issue>` - View ancestry, siblings, dependencies")
 	fmt.Println("- `bd close <issue>` - Mark issue complete")
 	fmt.Println("- `gt done` - Signal work ready for merge")
 	fmt.Println()
@@ -200,6 +202,7 @@ func outputCrewContext(ctx RoleContext) {
 	fmt.Println("- `gt mail inbox` - Check your inbox")
 	fmt.Println("- `bd ready` - Available issues")
 	fmt.Println("- `bd show <issue>` - View issue details")
+	fmt.Println("- `bd tree <issue>` - View ancestry, siblings, dependencies")
 	fmt.Println("- `bd close <issue>` - Mark issue complete")
 	fmt.Println()
 	fmt.Println("## Hookable Mail")