Add CalDAV calendar integration, LLM-suggested tags, and settings refinements

- CalDAV integration: per-user calendar config, create/list/search events
  via caldav library, LLM tools for calendar operations from chat
- LLM-suggested tags: new tag_suggestions service prompts LLM with existing
  tags and note content to suggest 3-5 relevant tags; exposed via API
  endpoints (suggest-tags, append-tag); integrated into editor views
  (suggest button + clickable pills) and chat tool calls (pills in
  ToolCallCard with one-click apply)
- Settings/model UI refinements, generation task improvements

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

frontend/src/components/DashboardChatInput.vue

@@ -1,17 +1,15 @@
 <script setup lang="ts">
-import { ref, watch, nextTick } from "vue";
+import { ref, nextTick } from "vue";
 import { apiGet } from "@/api/client";
 import { useChatStore } from "@/stores/chat";
-import ModelSelector from "@/components/ModelSelector.vue";
 import type { Note } from "@/types/note";
 
 const emit = defineEmits<{
-  submit: [payload: { content: string; model: string; contextNoteId?: number }];
+  submit: [payload: { content: string; contextNoteId?: number }];
 }>();
 
 const store = useChatStore();
 
-const selectedModel = ref(store.defaultModel || "");
 const messageInput = ref("");
 const inputEl = ref<HTMLTextAreaElement | null>(null);
 
@@ -23,20 +21,11 @@ const noteSearchResults = ref<{ id: number; title: string }[]>([]);
 const noteSearchLoading = ref(false);
 let noteSearchTimer: ReturnType<typeof setTimeout> | null = null;
 
-// Sync default model when store updates
-watch(
-  () => store.defaultModel,
-  (v) => {
-    if (!selectedModel.value && v) selectedModel.value = v;
-  }
-);
-
 function onSubmit() {
   const content = messageInput.value.trim();
   if (!content) return;
   emit("submit", {
     content,
-    model: selectedModel.value,
     contextNoteId: attachedNote.value?.id,
   });
   messageInput.value = "";
@@ -127,8 +116,6 @@ function removeAttachedNote() {
     </div>
 
     <div class="chat-input-bar">
-      <ModelSelector v-model="selectedModel" :disabled="!store.chatReady" />
-
       <div class="note-picker-wrapper">
         <button
           class="btn-attach"