drop dead pql.decisions.coverage IPC command

The 'pql decisions coverage' subcommand was removed in pql 1.4.x — the
replacement is the 'coverage_gaps' field on 'pql plan status'. No
production callers used this IPC surface; only the unit test referenced
it.

Removes the IPC registration, the PqlClient helper, and the matching
test case. Net negative LOC.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/src/daemon/pql_commands.dart

@@ -169,15 +169,6 @@ void registerPqlCommands(DaemonDispatcher d, PqlClient pql) {
     }
   });
 
-  d.register('pql.decisions.coverage', (req) async {
-    try {
-      final gaps = await pql.decisionCoverage();
-      return IpcResponse.ok(id: req.id, data: {'gaps': gaps});
-    } on PqlException catch (e) {
-      return _pqlError(req.id, e);
-    }
-  });
-
   d.register('pql.tickets.list', (req) async {
     try {
       final results = await pql.ticketList(

lib/src/pql/client.dart

@@ -106,10 +106,6 @@ class PqlClient {
     return _runObject(['decisions', 'read', id]);
   }
 
-  Future<List<Map<String, Object?>>> decisionCoverage() async {
-    return _runList(['decisions', 'coverage']);
-  }
-
   Future<List<Map<String, Object?>>> ticketList({
     String? status,
     String? team,