M7: add verbose mode for debugging

Add -v/--verbose persistent flag that prints debug info to stderr:
D-Bus connection status, token plugin directory discovery, unlock method
sequencing with per-method success/failure, and full cryptsetup command
lines including LD_LIBRARY_PATH.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/udisks/client.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 
+	"git.wntrmute.dev/kyle/arca/internal/verbose"
 	"github.com/godbus/dbus/v5"
 )
 
@@ -18,6 +19,7 @@ func NewClient() (*Client, error) {
 	if err != nil {
 		return nil, fmt.Errorf("cannot connect to udisks2 — is the udisks2 service running? (%w)", err)
 	}
+	verbose.Printf("connected to system D-Bus")
 	return &Client{conn: conn}, nil
 }