Add weather to agenda header and timeline via OpenMeteo

Shows daily weather summary (icon, description, high/low) in the agenda
section header, and hourly temperatures alongside the timeline hour ticks.
Weather data fetched from OpenMeteo (no API key needed), configured via
location coordinates in the plugin settings.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config.sample.json

@@ -14,6 +14,10 @@
           "task_tag_id": "your-task-tag-node-id",
           "due_date_field_id": "your-due-date-field-id"
         },
+        "location": {
+          "latitude": 48.8566,
+          "longitude": 2.3522
+        },
         "donetick": {
           "token": "your-donetick-access-token",
           "user_id": 1