feat(trust): full Duniter web-of-trust membership (params + referents)

Slice 4 of Block 2. The pure rule was already parameterised; this adds the
policy, cold-start and UI around it.

- commons_core: WotParams (sigQty/stepMax/sigValidity, Duniter defaults) +
  WebOfTrust.membersWith; npubToHex helper (NIP-19 decode) for adding roots.
- WotSettings (keystore): the active parameters, configurable — a young
  network loosens them and tightens as it grows, as Ğ1 did. Defaults Duniter.
- TrustReferents: the bootstrap 'seeds' membership is measured from — a
  bundled asset (empty until real founders are curated, no invented keys)
  unioned with referents the user adds by npub/QR. Honest cold-start.
- TrustCubit: computes the full membership verdict against referents+params
  alongside the personal circle, and exposes a TrustTier (networkMember >
  inYourCircle > vouched > unknown). Certifications issued with the active
  validity (they expire and renew, Duniter rule).
- UI: chat trust badge by tier; a 'Network of trust' screen (manage roots +
  advanced params) reached from the profile. i18n en/es/pt/ast.

Tests: WotParams/membersWith, npubToHex, TrustReferents, WotSettings, and
TrustCubit tiers/membership. Resolves the WoT-parameters decision
(open-decisions §B). Trust net stays empty/undetermined until seeded — by
design; users bootstrap their own roots.

apps/app_seeds/lib/ui/chat_screen.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:commons_core/commons_core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
@@ -10,6 +11,8 @@ import '../services/message_store.dart';
 import '../services/profile_cache.dart';
 import '../services/social_service.dart';
 import '../services/social_settings.dart';
+import '../services/trust_referents.dart';
+import '../services/wot_settings.dart';
 import '../state/messages_cubit.dart';
 import '../state/trust_cubit.dart';
 import 'theme.dart';
@@ -24,6 +27,8 @@ class ChatScreen extends StatefulWidget {
     required this.peerPubkey,
     this.messageStore,
     this.profileCache,
+    this.trustReferents,
+    this.wotSettings,
     super.key,
   });
 
@@ -37,6 +42,10 @@ class ChatScreen extends StatefulWidget {
   /// Optional cache of peer display names; null in tests.
   final ProfileCache? profileCache;
 
+  /// Web-of-trust bootstrap referents + parameters, for the membership verdict.
+  final TrustReferents? trustReferents;
+  final WotSettings? wotSettings;
+
   @override
   State<ChatScreen> createState() => _ChatScreenState();
 }
@@ -69,6 +78,9 @@ class _ChatScreenState extends State<ChatScreen> {
       }
     }
     final cachedName = await widget.profileCache?.name(widget.peerPubkey);
+    final referents = await widget.trustReferents?.all() ?? const <String>{};
+    final wotParams =
+        await widget.wotSettings?.params() ?? WotParams.duniter;
     if (!mounted) {
       await session?.close();
       return;
@@ -80,8 +92,13 @@ class _ChatScreenState extends State<ChatScreen> {
       selfPubkey: self,
       store: widget.messageStore,
     )..start();
-    final trust = TrustCubit(session?.trust,
-        peerPubkey: widget.peerPubkey, selfPubkey: self);
+    final trust = TrustCubit(
+      session?.trust,
+      peerPubkey: widget.peerPubkey,
+      selfPubkey: self,
+      referents: referents,
+      params: wotParams,
+    );
     unawaited(trust.load());
     setState(() {
       _session = session;
@@ -249,30 +266,33 @@ class _TrustBanner extends StatelessWidget {
       builder: (context, state) {
         final cubit = context.read<TrustCubit>();
         if (!cubit.isOnline || state.loading) return const SizedBox.shrink();
-        final known = state.knownToYou;
+        // Strongest applicable signal decides the badge (member > circle >
+        // vouched > unknown).
+        final (IconData icon, String label, bool strong) = switch (state.tier) {
+          TrustTier.networkMember => (Icons.verified, t.trust.member, true),
+          TrustTier.inYourCircle => (Icons.verified_user, t.trust.circle, true),
+          TrustTier.vouched => (
+              Icons.people_outline,
+              t.trust.count(n: state.certifierCount),
+              false,
+            ),
+          TrustTier.unknown => (Icons.person_outline, t.trust.none, false),
+        };
         return Container(
           width: double.infinity,
           color: seedPrimaryContainer.withValues(alpha: 0.5),
           padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
           child: Row(
             children: [
-              Icon(
-                known ? Icons.verified : Icons.verified_user_outlined,
-                size: 18,
-                color: seedGreen,
-              ),
+              Icon(icon, size: 18, color: strong ? seedGreen : seedMuted),
               const SizedBox(width: 8),
               Expanded(
                 child: Text(
-                  known
-                      ? t.trust.circle
-                      : state.certifierCount == 0
-                          ? t.trust.none
-                          : t.trust.count(n: state.certifierCount),
+                  label,
                   style: TextStyle(
-                    color: known ? seedGreen : seedOnSurface,
+                    color: strong ? seedGreen : seedOnSurface,
                     fontSize: 13,
-                    fontWeight: known ? FontWeight.w600 : FontWeight.w400,
+                    fontWeight: strong ? FontWeight.w600 : FontWeight.w400,
                   ),
                 ),
               ),