feat(plantare): UI — propose from chat, review & sign on the ledger

The viral loop, made usable end-to-end:

- Propose sheet (plantare_propose_sheet.dart): from a chat with a peer
  (their key already in hand), pick your side, name the seed, choose what
  comes back (similar · non-GMO organic / work hours / other) and an
  optional return-by, then sign and send. Reached from the chat overflow
  menu; confirms "waiting for them to sign".
- Plantares screen: incoming proposals show Accept & sign / Decline right
  on the tile; every bilateral row wears a handshake badge — awaiting
  signature, signed by both, or declined. Accept falls back to a gentle
  "offline" nudge if the proposal isn't in hand yet.
- i18n: full en + es for the bilateral flow; other locales fall back to
  base per slang config.

Wire-up only touches human copy (no jargon) and stays behind the
optional PlantareService, so inventory-only builds are unaffected.

Tests: propose sheet drives a real sign+send; the ledger renders the
signed/awaiting badges. Fake SocialSession in your_people test gains the
new transport getter. Widget tests targeted + timed. All green.

apps/app_seeds/lib/ui/chat_screen.dart

@@ -12,6 +12,7 @@ import '../domain/message_rules.dart';
 import '../i18n/strings.g.dart';
 import '../services/message_store.dart';
 import '../services/onboarding_store.dart';
+import '../services/plantare_service.dart';
 import '../services/profile_cache.dart';
 import '../services/profile_store.dart';
 import '../services/social_connection.dart';
@@ -23,6 +24,7 @@ import '../state/peer_rating_cubit.dart';
 import '../state/trust_cubit.dart';
 import 'market_gate.dart';
 import 'peer_avatar.dart';
+import 'plantare_propose_sheet.dart';
 import 'rating_sheet.dart';
 import 'report_sheet.dart';
 import 'theme.dart';
@@ -205,6 +207,23 @@ class _ChatScreenState extends State<ChatScreen> {
 
   /// Reports this peer (a standard report event to the community servers);
   /// when they were also blocked from the sheet, leaves the chat too.
+  /// Opens the "propose a signed Plantaré" sheet against this peer (their key is
+  /// in hand from the conversation), and confirms when a proposal is sent.
+  Future<void> _proposePlantare() async {
+    if (!getIt.isRegistered<PlantareService>()) return;
+    final sent = await showProposePlantareSheet(
+      context,
+      service: getIt<PlantareService>(),
+      peerPubkey: widget.peerPubkey,
+      peerName: _peerName,
+    );
+    if (sent == true && mounted) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(context.t.plantare.sent)),
+      );
+    }
+  }
+
   Future<void> _reportPeer() async {
     final outcome = await showReportSheet(
       context,
@@ -305,10 +324,16 @@ class _ChatScreenState extends State<ChatScreen> {
           PopupMenuButton<String>(
             key: const Key('chat.menu'),
             onSelected: (value) {
+              if (value == 'plantare') _proposePlantare();
               if (value == 'report') _reportPeer();
               if (value == 'block') _blockPeer();
             },
             itemBuilder: (context) => [
+              if (getIt.isRegistered<PlantareService>())
+                PopupMenuItem(
+                  value: 'plantare',
+                  child: Text(t.plantare.propose),
+                ),
               PopupMenuItem(
                 value: 'report',
                 child: Text(t.report.person),