fix: ZFC improvements - query tmux directly instead of marker TTL

Two ZFC fixes:

1. Boot marker file (hq-zee5n): Changed IsRunning() to query
   tmux.HasSession() directly instead of checking marker file
   freshness with TTL. Removed stale marker check from doctor.

2. Branch pattern matching (hq-zwuh6): Replaced hardcoded "polecat/"
   strings with constants.BranchPolecatPrefix for consistency.

Also removed 60-second WaitForCommand blocking from crew Start()
which was causing gt crew start to hang.

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

internal/cmd/mq_submit.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/spf13/cobra"
 	"github.com/steveyegge/gastown/internal/beads"
+	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/git"
 	"github.com/steveyegge/gastown/internal/rig"
 	"github.com/steveyegge/gastown/internal/style"
@@ -32,7 +33,7 @@ func parseBranchName(branch string) branchInfo {
 	info := branchInfo{Branch: branch}
 
 	// Try polecat/<worker>/<issue> format
-	if strings.HasPrefix(branch, "polecat/") {
+	if strings.HasPrefix(branch, constants.BranchPolecatPrefix) {
 		parts := strings.SplitN(branch, "/", 3)
 		if len(parts) == 3 {
 			info.Worker = parts[1]