Fix BASE_URL config loading, add tasks/projects; robust .env path resolution

- Config: try ENV_FILE, .env, ../.env for loading; trim trailing slash from BaseURL
- Log BASE_URL at server startup for verification
- .env.example: document BASE_URL
- Tasks, projects, tags, migrations and related API/handlers

Made-with: Cursor

internal/api/openapi/specs/base.json

@@ -33,7 +33,11 @@
     { "name": "Availability", "description": "Calendar availability queries" },
     { "name": "Booking", "description": "Public booking links and reservations" },
     { "name": "ICS", "description": "ICS calendar import and export" },
-    { "name": "Subscriptions", "description": "Calendar subscriptions (external iCal feeds)" }
+    { "name": "Subscriptions", "description": "Calendar subscriptions (external iCal feeds)" },
+    { "name": "Tasks", "description": "Task and to-do management" },
+    { "name": "Projects", "description": "Project/list grouping for tasks" },
+    { "name": "Tags", "description": "Tag management for tasks" },
+    { "name": "Webhooks", "description": "Task webhook configuration" }
   ],
   "security": [
     { "BearerAuth": [] },