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/tools.py

@@ -98,19 +98,19 @@ _CALDAV_TOOLS = [
                 "properties": {
                     "title": {
                         "type": "string",
-                        "description": "The event title",
+                        "description": "A descriptive event title (e.g. 'John's Birthday' not just 'Birthday')",
                     },
                     "start": {
                         "type": "string",
-                        "description": "Start date/time in ISO 8601 format (e.g. 2025-01-15T14:00:00)",
+                        "description": "Start date (YYYY-MM-DD for all-day) or datetime (ISO 8601, e.g. 2025-01-15T14:00:00)",
                     },
                     "end": {
                         "type": "string",
-                        "description": "Optional end date/time in ISO 8601 format",
+                        "description": "Optional end date or datetime in same format as start",
                     },
                     "duration": {
                         "type": "integer",
-                        "description": "Optional duration in minutes (default 60, ignored if end is set)",
+                        "description": "Optional duration in minutes (default 60, ignored if end is set or all_day is true)",
                     },
                     "description": {
                         "type": "string",
@@ -120,6 +120,14 @@ _CALDAV_TOOLS = [
                         "type": "string",
                         "description": "Optional event location",
                     },
+                    "all_day": {
+                        "type": "boolean",
+                        "description": "Set to true for all-day events like birthdays, holidays, deadlines (default false)",
+                    },
+                    "recurrence": {
+                        "type": "string",
+                        "description": "Optional iCalendar RRULE (e.g. 'FREQ=YEARLY' for annual, 'FREQ=WEEKLY' for weekly, 'FREQ=MONTHLY' for monthly)",
+                    },
                 },
                 "required": ["title", "start"],
             },
@@ -264,6 +272,8 @@ async def execute_tool(user_id: int, tool_name: str, arguments: dict) -> dict:
                 duration=arguments.get("duration"),
                 description=arguments.get("description"),
                 location=arguments.get("location"),
+                all_day=arguments.get("all_day", False),
+                recurrence=arguments.get("recurrence"),
             )
             return {
                 "success": True,