fix: gt commands follow .beads/redirect for shared beads (gt-ln5af)

Added ResolveBeadsDir() helper that follows .beads/redirect files,
enabling crew workers and polecats to properly access shared beads.

Updated callers:
- mailbox.go: NewMailboxFromAddress follows redirect
- catalog.go: LoadCatalog follows redirect at all levels
- doctor checks: beads_check, patrol_check, wisp_check follow redirect

Also added comprehensive tests for the redirect resolution logic.

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

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

internal/mail/mailbox.go

@@ -10,6 +10,8 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+
+	"github.com/steveyegge/gastown/internal/beads"
 )
 
 // Common errors
@@ -46,8 +48,9 @@ func NewMailboxBeads(identity, workDir string) *Mailbox {
 }
 
 // NewMailboxFromAddress creates a beads-backed mailbox from a GGT address.
+// Follows .beads/redirect for crew workers and polecats using shared beads.
 func NewMailboxFromAddress(address, workDir string) *Mailbox {
-	beadsDir := filepath.Join(workDir, ".beads")
+	beadsDir := beads.ResolveBeadsDir(workDir)
 	return &Mailbox{
 		identity: addressToIdentity(address),
 		workDir:  workDir,