feat: extract Gas Town types from beads core (bd-i54l)

Remove Gas Town-specific issue types (agent, role, rig, convoy, slot)
from beads core. These types are now identified by labels instead:
- gt:agent, gt:role, gt:rig, gt:convoy, gt:slot

Changes:
- internal/types/types.go: Remove TypeAgent, TypeRole, TypeRig, TypeConvoy, TypeSlot constants
- cmd/bd/agent.go: Create agents with TypeTask + gt:agent label
- cmd/bd/merge_slot.go: Create slots with TypeTask + gt:slot label
- internal/storage/sqlite/queries.go, transaction.go: Query convoys by gt:convoy label
- internal/rpc/server_issues_epics.go: Check gt:agent label for role_type/rig label auto-add
- cmd/bd/create.go: Check gt:agent label for role_type/rig label auto-add
- internal/ui/styles.go: Remove agent/role/rig type colors
- cmd/bd/export_obsidian.go: Remove agent/role/rig/convoy type tag mappings
- Update all affected tests

This enables beads to be a generic issue tracker while Gas Town
uses labels for its specific type semantics.

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

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

Executed-By: beads/crew/dave
Rig: beads
Role: crew

internal/types/types.go

@@ -412,6 +412,9 @@ func (s Status) IsValidWithCustom(customStatuses []string) bool {
 type IssueType string
 
 // Issue type constants
+// Note: Gas Town-specific types (agent, role, rig, convoy, slot) have been removed.
+// Use custom types via `bd config set types.custom "agent,role,..."` if needed.
+// These types are now identified by labels (gt:agent, gt:role, etc.) instead.
 const (
 	TypeBug          IssueType = "bug"
 	TypeFeature      IssueType = "feature"
@@ -422,18 +425,13 @@ const (
 	TypeMergeRequest IssueType = "merge-request" // Merge queue entry for refinery processing
 	TypeMolecule     IssueType = "molecule"      // Template molecule for issue hierarchies
 	TypeGate         IssueType = "gate"          // Async coordination gate
-	TypeAgent        IssueType = "agent"         // Agent identity bead
-	TypeRole         IssueType = "role"          // Agent role definition
-	TypeRig          IssueType = "rig"           // Rig identity bead (project container)
-	TypeConvoy       IssueType = "convoy"        // Cross-project tracking with reactive completion
 	TypeEvent        IssueType = "event"         // Operational state change record
-	TypeSlot         IssueType = "slot"          // Exclusive access slot (merge-slot gate)
 )
 
 // IsValid checks if the issue type value is valid (built-in types only)
 func (t IssueType) IsValid() bool {
 	switch t {
-	case TypeBug, TypeFeature, TypeTask, TypeEpic, TypeChore, TypeMessage, TypeMergeRequest, TypeMolecule, TypeGate, TypeAgent, TypeRole, TypeRig, TypeConvoy, TypeEvent, TypeSlot:
+	case TypeBug, TypeFeature, TypeTask, TypeEpic, TypeChore, TypeMessage, TypeMergeRequest, TypeMolecule, TypeGate, TypeEvent:
 		return true
 	}
 	return false
@@ -480,7 +478,7 @@ func (t IssueType) RequiredSections() []RequiredSection {
 			{Heading: "## Success Criteria", Hint: "Define high-level success criteria"},
 		}
 	default:
-		// Chore, message, molecule, gate, agent, role, convoy, event, merge-request
+		// Chore, message, molecule, gate, event, merge-request
 		// have no required sections
 		return nil
 	}

internal/types/types_test.go

@@ -401,12 +401,15 @@ func TestIssueTypeIsValid(t *testing.T) {
 		{TypeTask, true},
 		{TypeEpic, true},
 		{TypeChore, true},
-		{TypeAgent, true},
-		{TypeRole, true},
-		{TypeRig, true},
-		{TypeConvoy, true},
+		{TypeMessage, true},
+		{TypeMergeRequest, true},
+		{TypeMolecule, true},
+		{TypeGate, true},
 		{TypeEvent, true},
-		{TypeSlot, true},
+		// Gas Town types (agent, role, rig, convoy, slot) have been removed
+		// They are now identified by labels (gt:agent, etc.) instead
+		{IssueType("agent"), false},  // Now requires custom type config
+		{IssueType("convoy"), false}, // Now requires custom type config
 		{IssueType("invalid"), false},
 		{IssueType(""), false},
 	}
@@ -434,12 +437,9 @@ func TestIssueTypeRequiredSections(t *testing.T) {
 		{TypeMessage, 0, ""},
 		{TypeMolecule, 0, ""},
 		{TypeGate, 0, ""},
-		{TypeAgent, 0, ""},
-		{TypeRole, 0, ""},
-		{TypeRig, 0, ""},
-		{TypeConvoy, 0, ""},
 		{TypeEvent, 0, ""},
 		{TypeMergeRequest, 0, ""},
+		// Gas Town types (agent, role, rig, convoy, slot) have been removed
 	}
 
 	for _, tt := range tests {