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/components/AppLogo.vue

@@ -0,0 +1,49 @@
+<script setup lang="ts">
+defineProps<{ size?: number }>();
+</script>
+
+<template>
+  <svg
+    class="app-logo"
+    xmlns="http://www.w3.org/2000/svg"
+    viewBox="0 0 32 32"
+    :width="size ?? 24"
+    :height="size ?? 24"
+    aria-hidden="true"
+  >
+    <!-- Book body -->
+    <path class="logo-book" d="M4 7 C4 7 8 5 16 6 C24 5 28 7 28 7 L28 26 C28 26 24 24 16 25 C8 24 4 26 4 26 Z" stroke-width="0.5"/>
+    <!-- Book spine -->
+    <line class="logo-spine" x1="16" y1="6" x2="16" y2="25" stroke-width="0.8"/>
+    <!-- Left page lines -->
+    <line class="logo-lines" x1="7" y1="11" x2="14" y2="10.5" stroke-width="0.6" stroke-linecap="round"/>
+    <line class="logo-lines" x1="7" y1="14" x2="14" y2="13.5" stroke-width="0.6" stroke-linecap="round"/>
+    <line class="logo-lines" x1="7" y1="17" x2="14" y2="16.5" stroke-width="0.6" stroke-linecap="round"/>
+    <line class="logo-lines" x1="7" y1="20" x2="12" y2="19.5" stroke-width="0.6" stroke-linecap="round"/>
+    <!-- Right page lines -->
+    <line class="logo-lines" x1="18" y1="10.5" x2="25" y2="11" stroke-width="0.6" stroke-linecap="round"/>
+    <line class="logo-lines" x1="18" y1="13.5" x2="25" y2="14" stroke-width="0.6" stroke-linecap="round"/>
+    <line class="logo-lines" x1="18" y1="16.5" x2="25" y2="17" stroke-width="0.6" stroke-linecap="round"/>
+    <!-- Magic spark -->
+    <g transform="translate(24, 5)">
+      <path d="M0 -4 L1 -1 L4 0 L1 1 L0 4 L-1 1 L-4 0 L-1 -1 Z" fill="#f6ad55"/>
+      <path d="M0 -2.5 L0.6 -0.6 L2.5 0 L0.6 0.6 L0 2.5 L-0.6 0.6 L-2.5 0 L-0.6 -0.6 Z" fill="#fbd38d"/>
+    </g>
+    <!-- Secondary sparkles -->
+    <circle cx="20" cy="3" r="0.7" fill="#f6ad55" opacity="0.7"/>
+    <circle cx="27" cy="8" r="0.5" fill="#fbd38d" opacity="0.6"/>
+  </svg>
+</template>
+
+<style scoped>
+.logo-book {
+  fill: var(--color-text);
+  stroke: var(--color-text-secondary);
+}
+.logo-spine {
+  stroke: var(--color-text-secondary);
+}
+.logo-lines {
+  stroke: var(--color-text-muted);
+}
+</style>