Extract timing constants to constants package (gt-795e8)

Added 6 timing constants:
- ShutdownNotifyDelay (500ms)
- ClaudeStartTimeout (15s)
- ShellReadyTimeout (5s)
- DefaultDebounceMs (100)
- DefaultDisplayMs (5000)
- PollInterval (100ms)

Updated 7 files to use these constants instead of magic numbers.

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

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

internal/daemon/daemon.go

@@ -12,6 +12,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/keepalive"
 	"github.com/steveyegge/gastown/internal/polecat"
 	"github.com/steveyegge/gastown/internal/tmux"
@@ -547,7 +548,7 @@ func StopDaemon(townRoot string) error {
 	}
 
 	// Wait a bit for graceful shutdown
-	time.Sleep(500 * time.Millisecond)
+	time.Sleep(constants.ShutdownNotifyDelay)
 
 	// Check if still running
 	if err := process.Signal(syscall.Signal(0)); err == nil {

internal/daemon/lifecycle.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/steveyegge/gastown/internal/beads"
+	"github.com/steveyegge/gastown/internal/constants"
 	"github.com/steveyegge/gastown/internal/tmux"
 )
 
@@ -195,7 +196,7 @@ func (d *Daemon) executeLifecycleAction(request *LifecycleRequest) error {
 			d.logger.Printf("Killed session %s for restart", sessionName)
 
 			// Wait a moment
-			time.Sleep(500 * time.Millisecond)
+			time.Sleep(constants.ShutdownNotifyDelay)
 		}
 
 		// Restart the session