dynamic context panel tabs — spawn on demand, no empty placeholders

Context panel tabs are no longer static. Extensions spawn them
dynamically when relevant and despawn on deactivate:
- Tickets: detail tab spawns on builtin.tickets/selection
- Decisions: detail tab spawns on builtin.decisions/selection
- Backlinks: spawns when editor opens a file
- Markdown viewer: spawns when editor opens a .md file
- Graph: removed from static context (will be command-spawnable)

The icon rail only shows what's active — no empty tabs sitting
there waiting for content.

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

lib/builtin/pql/src/extension.dart

@@ -1,3 +1,5 @@
+import 'dart:async';
+
 import 'package:clide/builtin/pql/src/backlinks_view.dart';
 import 'package:clide/builtin/pql/src/pql_panel_view.dart';
 import 'package:clide/extension/extension.dart';
@@ -9,10 +11,14 @@ class PqlExtension extends ClideExtension {
   @override
   String get title => 'pql';
   @override
-  String get version => '0.1.0';
+  String get version => '0.2.0';
   @override
   List<String> get dependsOn => const [];
 
+  ClideExtensionContext? _ctx;
+  StreamSubscription<DaemonEvent>? _editorSub;
+  bool _backlinksSpawned = false;
+
   @override
   List<ContributionPoint> get contributions => [
         TabContribution(
@@ -24,14 +30,43 @@ class PqlExtension extends ClideExtension {
           priority: -60,
           build: (_) => const PqlPanelView(),
         ),
-        TabContribution(
-          id: 'pql.backlinks',
-          slot: Slots.contextPanel,
-          title: 'Links',
-          titleKey: 'tab.links',
-          i18nNamespace: id,
-          priority: -80,
-          build: (_) => const BacklinksView(),
-        ),
       ];
+
+  @override
+  Future<void> activate(ClideExtensionContext ctx) async {
+    _ctx = ctx;
+    _editorSub = ctx.events.on<DaemonEvent>().listen((e) {
+      if (e.subsystem != 'editor') return;
+      if (e.kind == 'editor.active-changed' || e.kind == 'editor.opened') {
+        _spawnBacklinks();
+      }
+    });
+  }
+
+  @override
+  Future<void> deactivate() async {
+    _editorSub?.cancel();
+    _despawnBacklinks();
+  }
+
+  void _spawnBacklinks() {
+    final ctx = _ctx;
+    if (ctx == null || _backlinksSpawned) return;
+    ctx.panels.contribute(TabContribution(
+      id: 'pql.backlinks',
+      slot: Slots.contextPanel,
+      title: 'Links',
+      priority: -80,
+      build: (_) => const BacklinksView(),
+    ));
+    _backlinksSpawned = true;
+    ctx.panels.activateTab(Slots.contextPanel, 'pql.backlinks');
+  }
+
+  void _despawnBacklinks() {
+    if (_backlinksSpawned) {
+      _ctx?.panels.uncontribute('pql.backlinks');
+      _backlinksSpawned = false;
+    }
+  }
 }