Add LLM tool calling for creating tasks, notes, and searching from chat

Ollama tool/function calling integration allows the LLM to create tasks,
create notes, and search existing notes on behalf of the user during chat.
Multi-round tool loop (max 5 rounds) lets the model execute tools then
produce a natural language response. Tool results are persisted in a new
JSONB column on messages and rendered as compact cards with linked titles.

- Migration 0013: add tool_calls JSONB column to messages
- New services/tools.py: tool definitions + execute_tool dispatcher
- llm.py: ChatChunk dataclass, stream_chat_with_tools(), date in system prompt
- generation_task.py: multi-round tool call loop with SSE tool_call events
- Frontend: ToolCallRecord type, streamingToolCalls in store, ToolCallCard
  component, rendering in ChatMessage and ChatView streaming bubble

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

frontend/src/components/ChatMessage.vue

@@ -2,6 +2,7 @@
 import { computed } from "vue";
 import { renderMarkdown } from "@/utils/markdown";
 import { useSettingsStore } from "@/stores/settings";
+import ToolCallCard from "@/components/ToolCallCard.vue";
 import type { Message } from "@/types/chat";
 
 const settingsStore = useSettingsStore();
@@ -48,6 +49,13 @@ const roleLabel = computed(() => {
           </div>
         </div>
         <div class="message-content prose" v-html="rendered"></div>
+        <div v-if="message.tool_calls?.length" class="tool-calls">
+          <ToolCallCard
+            v-for="(tc, i) in message.tool_calls"
+            :key="i"
+            :tool-call="tc"
+          />
+        </div>
         <div
           v-if="message.context_note_id"
           class="context-badge"
@@ -157,6 +165,12 @@ const roleLabel = computed(() => {
   color: #fff;
   border-color: var(--color-primary);
 }
+.tool-calls {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.3rem;
+  margin-top: 0.4rem;
+}
 .context-badge {
   margin-top: 0.4rem;
   font-size: 0.75rem;