Add multi-user auth, background generation, and chat UX improvements

Phase 5: Multi-user authentication with session cookies, bcrypt passwords,
first-user-is-admin pattern, per-user data isolation, backup/restore,
Docker Swarm production stack with secrets and network isolation.

Phase 5.1: Chat UX improvements:
- Background generation architecture (GenerationBuffer + asyncio task)
  with SSE fan-out, reconnect support, and periodic DB flushes
- LLM-generated conversation titles (first exchange + every 10th message)
- Stop generation button with cancel_event and partial content preservation
- Relative timestamps in sidebar (5m ago, 3h ago, then dates)
- Empty chat auto-cleanup on navigation away
- Save-as-note uses LLM for title generation, tags notes with "chat"
- Summarize-as-note also tags with "chat"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/stores/tasks.ts

@@ -1,6 +1,7 @@
 import { ref } from "vue";
 import { defineStore } from "pinia";
 import { apiGet, apiPost, apiPut, apiPatch, apiDelete } from "@/api/client";
+import { useToastStore } from "@/stores/toast";
 import type { Task, TaskListResponse, TaskStatus, TaskPriority } from "@/types/task";
 
 export const useTasksStore = defineStore("tasks", () => {
@@ -41,6 +42,9 @@ export const useTasksStore = defineStore("tasks", () => {
       );
       tasks.value = data.tasks;
       total.value = data.total;
+    } catch (e) {
+      useToastStore().show("Failed to load tasks", "error");
+      throw e;
     } finally {
       loading.value = false;
     }
@@ -50,6 +54,9 @@ export const useTasksStore = defineStore("tasks", () => {
     loading.value = true;
     try {
       currentTask.value = await apiGet<Task>(`/api/tasks/${id}`);
+    } catch (e) {
+      useToastStore().show("Failed to load task", "error");
+      throw e;
     } finally {
       loading.value = false;
     }
@@ -62,7 +69,12 @@ export const useTasksStore = defineStore("tasks", () => {
     priority?: TaskPriority;
     due_date?: string | null;
   }): Promise<Task> {
-    return await apiPost<Task>("/api/tasks", data);
+    try {
+      return await apiPost<Task>("/api/tasks", data);
+    } catch (e) {
+      useToastStore().show("Failed to create task", "error");
+      throw e;
+    }
   }
 
   async function updateTask(
@@ -71,31 +83,45 @@ export const useTasksStore = defineStore("tasks", () => {
       Pick<Task, "title" | "body" | "status" | "priority" | "due_date">
     >
   ): Promise<Task> {
-    const task = await apiPut<Task>(`/api/tasks/${id}`, data);
-    if (currentTask.value?.id === id) {
-      currentTask.value = task;
+    try {
+      const task = await apiPut<Task>(`/api/tasks/${id}`, data);
+      if (currentTask.value?.id === id) {
+        currentTask.value = task;
+      }
+      return task;
+    } catch (e) {
+      useToastStore().show("Failed to update task", "error");
+      throw e;
     }
-    return task;
   }
 
   async function patchStatus(id: number, status: TaskStatus): Promise<Task> {
-    const task = await apiPatch<Task>(`/api/tasks/${id}/status`, { status });
-    // Update in list if present
-    const idx = tasks.value.findIndex((t) => t.id === id);
-    if (idx !== -1) {
-      tasks.value[idx] = task;
+    try {
+      const task = await apiPatch<Task>(`/api/tasks/${id}/status`, { status });
+      const idx = tasks.value.findIndex((t) => t.id === id);
+      if (idx !== -1) {
+        tasks.value[idx] = task;
+      }
+      if (currentTask.value?.id === id) {
+        currentTask.value = task;
+      }
+      return task;
+    } catch (e) {
+      useToastStore().show("Failed to update task status", "error");
+      throw e;
     }
-    if (currentTask.value?.id === id) {
-      currentTask.value = task;
-    }
-    return task;
   }
 
   async function deleteTask(id: number) {
-    await apiDelete(`/api/tasks/${id}`);
-    tasks.value = tasks.value.filter((t) => t.id !== id);
-    if (currentTask.value?.id === id) {
-      currentTask.value = null;
+    try {
+      await apiDelete(`/api/tasks/${id}`);
+      tasks.value = tasks.value.filter((t) => t.id !== id);
+      if (currentTask.value?.id === id) {
+        currentTask.value = null;
+      }
+    } catch (e) {
+      useToastStore().show("Failed to delete task", "error");
+      throw e;
     }
   }