Replace internal todos with Vikunja API wrapper

- New app/vikunja.py: get_tasks, create_task, update_task, delete_task
- /todos page now reads from and writes to Vikunja (create, mark done, delete)
- Auto-todos (clean build plate, filament low) post to Vikunja after DB commit
- /api/todos router proxies to Vikunja
- .env.install: VIKUNJA_URL, VIKUNJA_API_TOKEN, VIKUNJA_PROJECT_ID

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

app/routers/todos.py

@@ -1,21 +1,24 @@
-from fastapi import APIRouter, Depends
-from sqlalchemy.orm import Session
-
-from app.db import get_db
-from app.models.todo import Todo
+from fastapi import APIRouter
+from app.vikunja import create_task, delete_task, get_tasks, update_task
 
 router = APIRouter(prefix="/todos", tags=["todos"])
 
 
 @router.get("/")
-def list_todos(db: Session = Depends(get_db)):
-    return [t.to_dict() for t in db.query(Todo).all()]
+def list_todos():
+    return get_tasks()
 
 
-@router.get("/{todo_id}")
-def get_todo(todo_id: int, db: Session = Depends(get_db)):
-    todo = db.query(Todo).filter(Todo.id == todo_id).first()
-    if not todo:
-        from fastapi import HTTPException
-        raise HTTPException(status_code=404, detail="Todo not found")
-    return todo.to_dict()
+@router.post("/")
+def create_todo(body: dict):
+    return create_task(body.get("title", ""))
+
+
+@router.post("/{task_id}")
+def update_todo(task_id: int, body: dict):
+    update_task(task_id, **body)
+
+
+@router.delete("/{task_id}")
+def delete_todo(task_id: int):
+    delete_task(task_id)