Add FIDO2/WebAuthn passkey authentication

Phase 14: Full WebAuthn support for passwordless passkey login and
hardware security key 2FA.

- go-webauthn/webauthn v0.16.1 dependency
- WebAuthnConfig with RPID/RPOrigin/DisplayName validation
- Migration 000009: webauthn_credentials table
- DB CRUD with ownership checks and admin operations
- internal/webauthn adapter: encrypt/decrypt at rest with AES-256-GCM
- REST: register begin/finish, login begin/finish, list, delete
- Web UI: profile enrollment, login passkey button, admin management
- gRPC: ListWebAuthnCredentials, RemoveWebAuthnCredential RPCs
- mciasdb: webauthn list/delete/reset subcommands
- OpenAPI: 6 new endpoints, WebAuthnCredentialInfo schema
- Policy: self-service enrollment rule, admin remove via wildcard
- Tests: DB CRUD, adapter round-trip, interface compliance
- Docs: ARCHITECTURE.md §22, PROJECT_PLAN.md Phase 14

Security: Credential IDs and public keys encrypted at rest with
AES-256-GCM via vault master key. Challenge ceremonies use 128-bit
nonces with 120s TTL in sync.Map. Sign counter validated on each
assertion to detect cloned authenticators. Password re-auth required
for registration (SEC-01 pattern). No credential material in API
responses or logs.

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

internal/ui/handlers_accounts.go

@@ -197,6 +197,15 @@ func (u *UIServer) handleAccountDetail(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
+	// Load WebAuthn credentials for the account detail page.
+	var webAuthnCreds []*model.WebAuthnCredential
+	if u.cfg.WebAuthnEnabled() {
+		webAuthnCreds, err = u.db.GetWebAuthnCredentials(acct.ID)
+		if err != nil {
+			u.logger.Warn("load webauthn credentials", "error", err)
+		}
+	}
+
 	u.render(w, "account_detail", AccountDetailData{
 		PageData:            PageData{CSRFToken: csrfToken, ActorName: u.actorName(r), IsAdmin: isAdmin(r)},
 		Account:             acct,
@@ -211,6 +220,9 @@ func (u *UIServer) handleAccountDetail(w http.ResponseWriter, r *http.Request) {
 		TokenDelegates:      tokenDelegates,
 		DelegatableAccounts: delegatableAccounts,
 		CanIssueToken:       true, // account_detail is admin-only, so admin can always issue
+		WebAuthnCreds:       webAuthnCreds,
+		DeletePrefix:        "/accounts/" + acct.UUID + "/webauthn",
+		WebAuthnEnabled:     u.cfg.WebAuthnEnabled(),
 	})
 }