fix(block2): back buttons on social screens + clear 'Share my seeds' button

Two UX reports:
- Market/Messages (and Profile/Chat) had no back button — they were opened with
  context.go (replaces the stack). Switched the drawer entries, home Market card,
  offer 'Message' link and inbox taps to context.push, so the AppBar shows a back
  arrow to return.
- The market's upload icon (tooltip-only) was unclear. Replaced it with a labelled
  FloatingActionButton.extended 'Share my seeds' (campaign icon); the config gear
  stays in the AppBar.

Analyzer clean.

apps/app_seeds/lib/ui/app_drawer.dart

@@ -41,7 +41,7 @@ class AppDrawer extends StatelessWidget {
               onTap: marketEnabled
                   ? () {
                       Navigator.of(context).pop();
-                      context.go('/market');
+                      context.push('/market');
                     }
                   : null,
             ),
@@ -51,7 +51,7 @@ class AppDrawer extends StatelessWidget {
               onTap: marketEnabled
                   ? () {
                       Navigator.of(context).pop();
-                      context.go('/profile');
+                      context.push('/profile');
                     }
                   : null,
             ),
@@ -61,7 +61,7 @@ class AppDrawer extends StatelessWidget {
               onTap: marketEnabled
                   ? () {
                       Navigator.of(context).pop();
-                      context.go('/messages');
+                      context.push('/messages');
                     }
                   : null,
             ),

apps/app_seeds/lib/ui/chat_list_screen.dart

@@ -65,7 +65,7 @@ class _ChatListScreenState extends State<ChatListScreen> {
                         maxLines: 1,
                         overflow: TextOverflow.ellipsis,
                       ),
-                      onTap: () => context.go('/chat/${c.peerPubkey}'),
+                      onTap: () => context.push('/chat/${c.peerPubkey}'),
                     );
                   },
                 ),

apps/app_seeds/lib/ui/home_screen.dart

@@ -87,7 +87,7 @@ class HomeScreen extends StatelessWidget {
                       subtitle: t.home.openMarketSubtitle,
                       tag: marketEnabled ? null : t.common.comingSoon,
                       onTap: marketEnabled
-                          ? () => context.go('/market')
+                          ? () => context.push('/market')
                           : null,
                     ),
                   ],

apps/app_seeds/lib/ui/market_screen.dart

@@ -148,13 +148,6 @@ class _MarketScreenState extends State<MarketScreen> {
       appBar: AppBar(
         title: Text(t.market.title),
         actions: [
-          if (cubit != null && (cubit.isOnline || widget.outbox != null))
-            IconButton(
-              key: const Key('market.shareMine'),
-              icon: const Icon(Icons.ios_share_outlined),
-              tooltip: t.market.shareMine,
-              onPressed: _shareMine,
-            ),
           IconButton(
             key: const Key('market.config'),
             icon: const Icon(Icons.tune),
@@ -163,6 +156,15 @@ class _MarketScreenState extends State<MarketScreen> {
           ),
         ],
       ),
+      floatingActionButton:
+          cubit != null && (cubit.isOnline || widget.outbox != null)
+              ? FloatingActionButton.extended(
+                  key: const Key('market.shareMine'),
+                  onPressed: _shareMine,
+                  icon: const Icon(Icons.campaign_outlined),
+                  label: Text(t.market.shareMine),
+                )
+              : null,
       body: _loading || cubit == null
           ? const Center(child: CircularProgressIndicator())
           : BlocProvider.value(
@@ -232,7 +234,7 @@ class MarketBody extends StatelessWidget {
             return _OfferCard(
               offer: o,
               mine: mine,
-              onContact: mine ? null : () => context.go('/chat/${o.authorPubkeyHex}'),
+              onContact: mine ? null : () => context.push('/chat/${o.authorPubkeyHex}'),
             );
           },
         );