feat: add optional completed filter to GET /tasks/ endpoint

[de9pk]

Summary

This PR implements Issue #3 — adds an optional completed query parameter to GET /tasks/ to filter tasks by their completion status.

Changes

crud.py

• Added from typing import Optional import
• Updated get_tasks() to accept an optional completed: Optional[bool] = None parameter
• When completed is provided, the query filters tasks where Task.completed == completed

routers/tasks.py

• Added Optional to imports
• Added completed: Optional[bool] = None query parameter to the GET /tasks/ endpoint
• Passes the completed value to crud.get_tasks()

Usage

# Get all tasks
GET /tasks/

# Get only completed tasks
GET /tasks/?completed=true

# Get only incomplete tasks
GET /tasks/?completed=false

Closes #3

[Navashub]

Great work @de9pk - this is a clean, focused PR that hits every requirement in Issue #3. The implementation correctly handles all three cases (completed=true, completed=false, no param), the filter composes correctly with the existing pagination, and I appreciate that you kept the query object pattern (query = db.query(...) then conditionally filter) rather than duplicating code. Branch name, commit prefix, and closing the issue via Closes #3 in the description - all done right. Merging now.