Add the plugin's SessionStart hook so a session learns its own id (issue 1744)

A session is never told its session id by any tool, only by a hook's
stdin, so it cannot name itself to claude_code_wait. The plugin's
SessionStart hook (claude-code session-start <waits-dir>) prints the id
and how to give it, plus the session's still-open waits after a /clear,
reading the waits file claude_code_wait mirrors directly rather than
calling back into this module. Carries the Stop hook's command and the
GuardFiles.WaitsDir plumbing MarketplaceWith needs for both (issue 1743
wires the Stop hook's dispatch next).

modules/claude-code/cmd/claude-code/main.go

@@ -417,6 +417,10 @@ func main() {
 	if len(os.Args) == 3 && os.Args[1] == "guard" {
 		os.Exit(runGuard(os.Args[2], os.Stdin, os.Stderr))
 	}
+	// The plugin's SessionStart hook (novox/hq ADR 0489 §1, issue 1744): names the session's id and its open waits.
+	if len(os.Args) == 3 && os.Args[1] == "session-start" {
+		os.Exit(runSessionStart(os.Args[2], os.Stdin, os.Stdout))
+	}
 	// The helper that touches the agent's home as the agent's account (novox/hq ADR 0266), started by this
 	// module through sudo: one answer per request on stdin, until it ends.
 	if len(os.Args) == 2 && os.Args[1] == HelperArg {