chore(frontend): real ESLint instead of a placeholder; fix hook order (FLAW-19)

eslint.config.js with the recommended JS/TypeScript rules and the React
hooks rules; npm run lint runs ESLint and is part of the image build.
Errors fail the build, the 24 exhaustive-deps findings stay warnings.

It found two real bugs: TaskDetailModal and ManageColumnsModal called
their hooks after 'if (!isOpen) return null', so the hook count changed
whenever the dialog opened or closed. Both are now a thin wrapper plus a
content component. Also removes unused imports and dead code (old task
list share handlers, an unused realtime status, an unused rollup).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/triage/TaskDetailModal.tsx

@@ -7,19 +7,16 @@ import {
   FileText,
   Plus,
   CheckSquare,
-  Clock,
-  Layers,
   Hash,
   AlertTriangle,
   Flame,
-  ChevronRight,
   Folder,
   Webhook,
   Lock,
   UserPlus,
   Repeat,
 } from 'lucide-react';
-import { Thought, SubTask, TaskList, TaskListMember, KanbanColumn, User, Recurrence } from '../../lib/types';
+import { Thought, TaskList, TaskListMember, KanbanColumn, User, Recurrence } from '../../lib/types';
 import { UserAvatar } from '../../components/UserAvatar';
 import { UserAutocomplete } from '../UserAutocomplete';
 import { triggerHaptic } from '../../lib/api';
@@ -51,9 +48,13 @@ interface TaskDetailModalProps {
   readOnly?: boolean; // Task belongs to a list shared with "viewer" permission
 }
 
-export const TaskDetailModal: React.FC<TaskDetailModalProps> = ({
+// The wrapper decides whether the dialog is shown; the content holds all hooks, so their number never
+// changes between renders (hooks after an early return break React when isOpen flips)
+export const TaskDetailModal: React.FC<TaskDetailModalProps> = (props) =>
+  props.isOpen && props.task ? <TaskDetailModalContent {...props} task={props.task} /> : null;
+
+const TaskDetailModalContent: React.FC<TaskDetailModalProps & { task: Thought }> = ({
   task,
-  isOpen,
   onClose,
   activeColumns,
   taskLists,
@@ -75,8 +76,6 @@ export const TaskDetailModal: React.FC<TaskDetailModalProps> = ({
   onDeleteTask,
   readOnly = false,
 }) => {
-  if (!isOpen || !task) return null;
-
   const [titleDraft, setTitleDraft] = useState(task.content);
   const [isEditingTitle, setIsEditingTitle] = useState(false);
 
@@ -144,7 +143,7 @@ export const TaskDetailModal: React.FC<TaskDetailModalProps> = ({
 
   const handleAddTagSubmit = async (e: React.FormEvent) => {
     e.preventDefault();
-    let cleaned = newTagDraft.trim().replace(/^#+/, '').toLowerCase();
+    const cleaned = newTagDraft.trim().replace(/^#+/, '').toLowerCase();
     if (!cleaned) return;
     const currentTags = Array.isArray(task.tags) ? [...task.tags] : [];
     if (!currentTags.includes(cleaned)) {
@@ -177,11 +176,6 @@ export const TaskDetailModal: React.FC<TaskDetailModalProps> = ({
     onUpdateDueDate(task, joinDue(addDays(daysOffset), splitDue(task.dueDate).time));
   };
 
-  const currentColumn = activeColumns.find((c) => c.id === task.kanbanStatus) ||
-    (task.isCompleted
-      ? activeColumns.find((c) => c.isDone) || activeColumns[activeColumns.length - 1]
-      : activeColumns.find((c) => !c.isDone) || activeColumns[0]);
-
   const subtasks = Array.isArray(task.subtasks) ? task.subtasks : [];
   const completedSubtasks = subtasks.filter((s) => s.isCompleted).length;
   const subtasksPercent = subtasks.length > 0 ? Math.round((completedSubtasks / subtasks.length) * 100) : 0;