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.

packages/commons_core/lib/commons_core.dart

@@ -14,6 +14,7 @@ export 'src/ids/id_gen.dart';
 export 'src/social/certification.dart';
 export 'src/social/geohash.dart';
 export 'src/social/message_transport.dart';
+export 'src/social/nostr_ids.dart';
 export 'src/social/nostr/nostr_channel.dart';
 export 'src/social/nostr/nostr_connection.dart';
 export 'src/social/nostr/nostr_message_transport.dart';

packages/commons_core/lib/src/social/nostr_ids.dart

@@ -0,0 +1,21 @@
+import 'package:nostr/nostr.dart';
+
+/// Decodes a NIP-19 `npub…` into its 64-char hex public key.
+///
+/// Accepts an already-hex key unchanged (so callers can take either form), and
+/// throws [FormatException] on anything that is neither. Used to add web-of-trust
+/// referents shared as an `npub` (or scanned from a QR).
+String npubToHex(String input) {
+  final value = input.trim();
+  if (_isHex64(value)) return value.toLowerCase();
+  if (!value.startsWith('npub1')) {
+    throw const FormatException('not an npub or hex public key');
+  }
+  final decoded = Nip19.decode(payload: value);
+  if (decoded.prefix != Nip19Prefix.npub || !_isHex64(decoded.data)) {
+    throw const FormatException('not an npub public key');
+  }
+  return decoded.data.toLowerCase();
+}
+
+bool _isHex64(String s) => RegExp(r'^[0-9a-fA-F]{64}$').hasMatch(s);

packages/commons_core/lib/src/social/web_of_trust.dart

@@ -1,5 +1,44 @@
+import 'package:equatable/equatable.dart';
+
 import 'certification.dart';
 
+/// The Duniter/Ğ1 web-of-trust parameters. Kept as data (not magic numbers) so
+/// they can be persisted and tuned as the network grows — a young network needs
+/// looser values than a mature one, exactly as Ğ1 itself started.
+///
+/// - [sigQty]: certifications from existing members needed to become a member.
+/// - [stepMax]: max certification hops from a bootstrap referent (seed).
+/// - [sigValidity]: how long a certification counts before it must be renewed.
+class WotParams extends Equatable {
+  const WotParams({
+    required this.sigQty,
+    required this.stepMax,
+    required this.sigValidity,
+  });
+
+  /// The Ğ1 reference values (sigQty 5, stepMax 5, ~1-year validity — Ğ1 uses a
+  /// longer window, but the seed app renews yearly to match `certify`'s default).
+  static const duniter = WotParams(
+    sigQty: 5,
+    stepMax: 5,
+    sigValidity: Duration(days: 365),
+  );
+
+  final int sigQty;
+  final int stepMax;
+  final Duration sigValidity;
+
+  WotParams copyWith({int? sigQty, int? stepMax, Duration? sigValidity}) =>
+      WotParams(
+        sigQty: sigQty ?? this.sigQty,
+        stepMax: stepMax ?? this.stepMax,
+        sigValidity: sigValidity ?? this.sigValidity,
+      );
+
+  @override
+  List<Object?> get props => [sigQty, stepMax, sigValidity];
+}
+
 /// Pure web-of-trust computation (Duniter/Ğ1 rules), Flutter-free and I/O-free.
 /// Answers "who counts as a known member" from certification edges, using two
 /// rules: **N certifications from existing members** (sigQty) and **within
@@ -76,6 +115,17 @@ class WebOfTrust {
       members(seeds: seeds, threshold: threshold, maxDistance: maxDistance)
           .contains(pubkey);
 
+  /// Members using a [WotParams] bundle (Duniter naming: sigQty/stepMax).
+  Set<String> membersWith({
+    required Set<String> seeds,
+    required WotParams params,
+  }) =>
+      members(
+        seeds: seeds,
+        threshold: params.sigQty,
+        maxDistance: params.stepMax,
+      );
+
   /// BFS hop-distance from the nearest seed over certification edges.
   Map<String, int> _distancesFromSeeds(Set<String> seeds) {
     final dist = <String, int>{for (final s in seeds) s: 0};