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/test/services/wot_settings_test.dart

@@ -0,0 +1,28 @@
+import 'package:commons_core/commons_core.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/services/wot_settings.dart';
+
+import '../support/test_support.dart';
+
+void main() {
+  late WotSettings settings;
+  setUp(() => settings = WotSettings(InMemorySecretStore()));
+
+  test('defaults to the Duniter parameters', () async {
+    expect(await settings.params(), WotParams.duniter);
+  });
+
+  test('persists saved parameters', () async {
+    const custom = WotParams(
+        sigQty: 3, stepMax: 4, sigValidity: Duration(days: 180));
+    await settings.save(custom);
+    expect(await settings.params(), custom);
+  });
+
+  test('reset restores the Duniter defaults', () async {
+    await settings.save(const WotParams(
+        sigQty: 1, stepMax: 1, sigValidity: Duration(days: 30)));
+    await settings.reset();
+    expect(await settings.params(), WotParams.duniter);
+  });
+}