Switch default model to qwen3 and add intent routing for reliable tool calling

Mistral didn't reliably use Ollama's structured tool calling API — it wrote
tool calls as JSON text instead of invoking them. This adds an intent routing
layer that classifies user intent via a fast non-streaming LLM call before
streaming, executing detected tools directly and bypassing native tool calling.

- Change default OLLAMA_MODEL from mistral to qwen3
- Add intent.py: classify_intent() with JSON parsing and fallback regex
- Integrate intent routing into generation_task.py round 0
- Add all-day event support (iCalendar DATE values) to CalDAV service
- Add recurring event support (RRULE) to CalDAV service and tool definition
- Improve create_event tool description for descriptive titles
- Enhance system prompt with structured tool usage guidance

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

src/fabledassistant/services/llm.py

@@ -245,18 +245,25 @@ async def build_context(
     assistant_name = await get_setting(user_id, "assistant_name", "Fable")
     today = date_type.today().isoformat()
     has_caldav = await is_caldav_configured(user_id)
-    date_guidance = "For relative dates like 'Friday' or 'next week', resolve them to YYYY-MM-DD format."
+
+    # Build tool usage guidance based on available integrations
+    tool_lines = [
+        "You have access to tool functions. You MUST use them when the user asks you to create, add, find, schedule, or search for anything.",
+        "CRITICAL: Call the tool functions directly. NEVER write out function calls as text or code. NEVER describe what you would do — just do it.",
+        "Available actions: create_task, create_note, search_notes.",
+    ]
     if has_caldav:
-        date_guidance += " For calendar events, use ISO 8601 datetime format (e.g. 2025-01-15T14:00:00)."
+        tool_lines[-1] = "Available actions: create_task, create_note, search_notes, create_event, list_events, search_events."
+        tool_lines.append("For calendar events, use ISO 8601 datetime format (e.g. 2026-09-30T00:00:00).")
+    tool_lines.append("For relative dates like 'Friday' or 'next week', resolve them to YYYY-MM-DD format.")
+    tool_guidance = "\n".join(tool_lines)
 
     system_parts = [
         f"You are a helpful assistant named {assistant_name}, integrated into a note-taking and task-tracking app called Fabled Assistant. "
         "Help users with their notes, tasks, and general questions. "
         "When note context is provided, use it to give relevant answers. "
-        f"Today's date is {today}. "
-        "When the user asks you to create, add, or find something, use the provided tool functions. "
-        "Do not describe or write out function calls as text — actually invoke the tools. "
-        f"{date_guidance}"
+        f"Today's date is {today}.\n\n"
+        f"{tool_guidance}"
     ]
 
     context_meta: dict = {