Add vault seal/unseal lifecycle

- New internal/vault package: thread-safe Vault struct with
  seal/unseal state, key material zeroing, and key derivation
- REST: POST /v1/vault/unseal, POST /v1/vault/seal,
  GET /v1/vault/status; health returns sealed status
- UI: /unseal page with passphrase form, redirect when sealed
- gRPC: sealedInterceptor rejects RPCs when sealed
- Middleware: RequireUnsealed blocks all routes except exempt
  paths; RequireAuth reads pubkey from vault at request time
- Startup: server starts sealed when passphrase unavailable
- All servers share single *vault.Vault by pointer
- CSRF manager derives key lazily from vault

Security: Key material is zeroed on seal. Sealed middleware
runs before auth. Handlers fail closed if vault becomes sealed
mid-request. Unseal endpoint is rate-limited (3/s burst 5).
No CSRF on unseal page (no session to protect; chicken-and-egg
with master key). Passphrase never logged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/ui/ui_test.go

@@ -17,7 +17,7 @@ import (
 	"git.wntrmute.dev/kyle/mcias/internal/config"
 	"git.wntrmute.dev/kyle/mcias/internal/db"
 	"git.wntrmute.dev/kyle/mcias/internal/model"
-	"git.wntrmute.dev/kyle/mcias/internal/token"
+	"git.wntrmute.dev/kyle/mcias/internal/vault"
 )
 
 const testIssuer = "https://auth.example.com"
@@ -48,7 +48,8 @@ func newTestUIServer(t *testing.T) *UIServer {
 	cfg := config.NewTestConfig(testIssuer)
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
 
-	uiSrv, err := New(database, cfg, priv, pub, masterKey, logger)
+	v := vault.NewUnsealed(masterKey, priv, pub)
+	uiSrv, err := New(database, cfg, v, logger)
 	if err != nil {
 		t.Fatalf("new UIServer: %v", err)
 	}
@@ -319,7 +320,7 @@ func issueAdminSession(t *testing.T, u *UIServer) (tokenStr, accountUUID string,
 	if err := u.db.SetRoles(acct.ID, []string{"admin"}, nil); err != nil {
 		t.Fatalf("SetRoles: %v", err)
 	}
-	tok, claims, err := token.IssueToken(u.privKey, testIssuer, acct.UUID, []string{"admin"}, time.Hour)
+	tok, claims, err := u.issueToken(acct.UUID, []string{"admin"}, time.Hour)
 	if err != nil {
 		t.Fatalf("IssueToken: %v", err)
 	}
@@ -645,7 +646,7 @@ func issueUserSession(t *testing.T, u *UIServer) string {
 	if err := u.db.SetRoles(acct.ID, []string{"user"}, nil); err != nil {
 		t.Fatalf("SetRoles: %v", err)
 	}
-	tok, claims, err := token.IssueToken(u.privKey, testIssuer, acct.UUID, []string{"user"}, time.Hour)
+	tok, claims, err := u.issueToken(acct.UUID, []string{"user"}, time.Hour)
 	if err != nil {
 		t.Fatalf("IssueToken: %v", err)
 	}