Redesign gt seance: ZFC-compliant literal seance with predecessors (gt-7qvd7)

Major redesign based on design review:

1. REMOVED: Claude Code internal parsing (ZFC violation)
   - Deleted internal/claude/sessions.go (parsed ~/.claude/projects/)
   - This coupled us to Claude Code's undocumented internal format

2. ADDED: Event-based session discovery
   - gt prime now emits session_start events to ~/gt/.events.jsonl
   - Events include role, session_id, topic, cwd
   - Discovery reads our own event stream (ZFC-compliant)

3. ADDED: --talk flag for actual seances
   - gt seance --talk <session-id> spawns: claude --fork-session --resume <id>
   - --fork-session creates a new session (read-only, no grave disturbance)
   - You literally talk to your predecessor: "Where did you put X?"

4. ADDED: One-shot prompt mode
   - gt seance --talk <id> -p "Where is the config?"
   - Uses claude --print for quick questions

The name "seance" is now literal - you commune with the dead (past sessions).

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

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

internal/events/events.go

@@ -46,6 +46,10 @@ const (
 	TypeBoot    = "boot"
 	TypeHalt    = "halt"
 
+	// Session events (for seance discovery)
+	TypeSessionStart = "session_start"
+	TypeSessionEnd   = "session_end"
+
 	// Witness patrol events
 	TypePatrolStarted   = "patrol_started"
 	TypePolecatChecked  = "polecat_checked"
@@ -269,3 +273,22 @@ func HaltPayload(services []string) map[string]interface{} {
 		"services": services,
 	}
 }
+
+// SessionPayload creates a payload for session start/end events.
+// sessionID: Claude Code session UUID
+// role: Gas Town role (e.g., "gastown/crew/joe", "deacon")
+// topic: What the session is working on
+// cwd: Working directory
+func SessionPayload(sessionID, role, topic, cwd string) map[string]interface{} {
+	p := map[string]interface{}{
+		"session_id": sessionID,
+		"role":       role,
+	}
+	if topic != "" {
+		p["topic"] = topic
+	}
+	if cwd != "" {
+		p["cwd"] = cwd
+	}
+	return p
+}