Add invitation system, table of contents, actionable dashboard, and settings improvements

Invitation system (Phase 5.7):
- invitation_tokens table (migration 0012) with SHA256-hashed tokens, 7-day expiry
- Admin CRUD endpoints: POST/GET/DELETE /api/admin/invitations
- Branded invitation email with registration link
- /register-invite frontend view with token validation and account creation
- Admin UI: invite form + pending invitations table with revoke
- Configurable base URL setting for email links (replaces hardcoded Config.BASE_URL)

Table of contents + markdown improvements (Phase 5.8):
- TableOfContents component: sticky sidebar, heading parsing, smooth-scroll
- Custom marked renderer adds id attributes to headings for anchor links
- stripFirstLineTags() prevents leading #tags from rendering as headings
- NoteViewerView/TaskViewerView flex layout with TOC sidebar (hidden ≤1200px)
- Model catalog refresh: added llama3.2/3.3, gemma3, qwen3, phi4, deepseek-r1,
  qwen2.5-coder, dolphin3; added Reasoning category; removed discontinued models
- Settings model section split into Installed/Available tabs

Actionable dashboard (Phase 5.9):
- due_before/due_after query params on /api/tasks (exclusive < / inclusive >=)
- HomeView rewritten: overdue (red accent), due today, in progress, chats, notes
- 5 parallel API calls via Promise.allSettled
- Client-side done filtering and in-progress deduplication
- Task sections hidden when empty; status toggle removes done tasks

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

frontend/src/components/TableOfContents.vue

@@ -0,0 +1,83 @@
+<script setup lang="ts">
+import { computed } from "vue";
+import { slugify } from "@/utils/markdown";
+
+const props = defineProps<{ body: string }>();
+
+interface TocEntry {
+  depth: number;
+  text: string;
+  id: string;
+}
+
+const headings = computed<TocEntry[]>(() => {
+  const entries: TocEntry[] = [];
+  const re = /^(#{1,6})\s+(.+)$/gm;
+  let match;
+  while ((match = re.exec(props.body)) !== null) {
+    entries.push({
+      depth: match[1].length,
+      text: match[2].trim(),
+      id: slugify(match[2].trim()),
+    });
+  }
+  return entries;
+});
+
+function scrollTo(id: string) {
+  const el = document.getElementById(id);
+  if (el) el.scrollIntoView({ behavior: "smooth" });
+}
+</script>
+
+<template>
+  <nav v-if="headings.length" class="toc">
+    <h3 class="toc-title">Contents</h3>
+    <ul class="toc-list">
+      <li
+        v-for="(h, i) in headings"
+        :key="i"
+        :style="{ paddingLeft: (h.depth - 1) * 0.75 + 'rem' }"
+      >
+        <a class="toc-link" @click.prevent="scrollTo(h.id)" :href="`#${h.id}`">
+          {{ h.text }}
+        </a>
+      </li>
+    </ul>
+  </nav>
+</template>
+
+<style scoped>
+.toc {
+  position: sticky;
+  top: 1rem;
+  width: 200px;
+  flex-shrink: 0;
+  align-self: flex-start;
+  font-size: 0.85rem;
+  line-height: 1.4;
+}
+.toc-title {
+  font-size: 0.8rem;
+  text-transform: uppercase;
+  color: var(--color-text-muted);
+  margin: 0 0 0.5rem;
+  letter-spacing: 0.05em;
+}
+.toc-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
+.toc-list li {
+  margin-bottom: 0.25rem;
+}
+.toc-link {
+  color: var(--color-text-muted);
+  text-decoration: none;
+  cursor: pointer;
+}
+.toc-link:hover {
+  color: var(--color-primary);
+}
+</style>