feat(tenant): promote internal/tenant to pkg/tenant for external imports

The tenant.Config primitive is the public contract that downstream
shim repos (liquidity/bridge, hanzo/bridge-shim, zoo/bridge-shim,
pars/bridge-shim) consume to validate their own tenant.yaml. Keeping
it under internal/ blocked that — shims couldn't import it.

This patch moves the package one directory level (internal/tenant →
pkg/tenant), updates the three call-sites in cmd/bridge, and changes
nothing else. All tests still pass.

Tests:
- ./pkg/tenant 26 tests, PASS
- ./cmd/bridge full suite PASS

cmd/bridge/main.go

@@ -51,7 +51,7 @@ import (
 	"github.com/luxfi/bridge/internal/depositcheck"
 	"github.com/luxfi/bridge/internal/mchain"
 	"github.com/luxfi/bridge/internal/substrate"
-	"github.com/luxfi/bridge/internal/tenant"
+	"github.com/luxfi/bridge/pkg/tenant"
 	"github.com/luxfi/bridge/internal/tokens"
 	"github.com/luxfi/bridge/internal/txassembler"
 	luxlog "github.com/luxfi/log"

cmd/bridge/main_test.go

@@ -7,7 +7,7 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/luxfi/bridge/internal/tenant"
+	"github.com/luxfi/bridge/pkg/tenant"
 )
 
 // Coverage for the small helpers in main.go. The main() function itself

cmd/bridge/tenant_overrides.go

@@ -3,7 +3,7 @@ package main
 import (
 	"flag"
 
-	"github.com/luxfi/bridge/internal/tenant"
+	"github.com/luxfi/bridge/pkg/tenant"
 )
 
 // applyTenantOverrides patches flag pointers with values from the