decision detail shows full markdown body via pql decisions read

New pql.decisions.read IPC verb returns the full markdown section
body. Decision detail view now shows: title card, full decision
text (rationale, cost, cross-references), and clickable ref cards
for cross-reference navigation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/src/pql/client.dart

@@ -94,6 +94,10 @@ class PqlClient {
     return _runObject(args);
   }
 
+  Future<Map<String, Object?>> decisionRead(String id) async {
+    return _runObject(['decisions', 'read', id]);
+  }
+
   Future<List<Map<String, Object?>>> decisionCoverage() async {
     return _runList(['decisions', 'coverage']);
   }