fix: Use rig's configured prefix for agent bead IDs (gt-kdy77, gt-ihvq0)

Added WithPrefix variants to agent bead ID functions:
- AgentBeadIDWithPrefix(prefix, rig, role, name)
- WitnessBeadIDWithPrefix, RefineryBeadIDWithPrefix
- CrewBeadIDWithPrefix, PolecatBeadIDWithPrefix

Updated callers to use rig's configured prefix:
- crew_add.go: reads r.Config.Prefix for crew worker beads
- rig/manager.go: uses prefix param for witness/refinery beads
- doctor/agent_beads_check.go: uses prefix from routes.jsonl

This allows non-gastown rigs (like beads with bd- prefix) to have
properly-prefixed agent beads.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/rig/manager.go

@@ -417,13 +417,13 @@ func (m *Manager) initAgentBeads(rigPath, rigName, prefix string, isFirstRig boo
 	// Always create rig-specific agents (using canonical naming: prefix-rig-role-name)
 	agents = append(agents,
 		agentDef{
-			id:       beads.WitnessBeadID(rigName),
+			id:       beads.WitnessBeadIDWithPrefix(prefix, rigName),
 			roleType: "witness",
 			rig:      rigName,
 			desc:     fmt.Sprintf("Witness for %s - monitors polecat health and progress.", rigName),
 		},
 		agentDef{
-			id:       beads.RefineryBeadID(rigName),
+			id:       beads.RefineryBeadIDWithPrefix(prefix, rigName),
 			roleType: "refinery",
 			rig:      rigName,
 			desc:     fmt.Sprintf("Refinery for %s - processes merge queue.", rigName),