Add ?page= and ?limit= pagination to GET /tasks

[daniel-sarosi-gwc]

Goal

Paginate the list endpoint so callers don't have to receive the full list.

Acceptance criteria

• GET /tasks?limit=10 returns at most 10 tasks.
• GET /tasks?page=2&limit=10 returns tasks 11–20 (1-indexed pages).
• Default page=1, default limit=50 (document the choice in code).
• Out-of-range pages return an empty array, not an error.
• Reject page=0 and limit=0 with 400 Bad Request.
• Tests cover: default page, second page, last partial page, page beyond the end.

Branch

feat/issue-3-add-pagination

Files to touch

• src/handlers.rs — extract Query<Pagination>; return the slice.
• src/store.rs — add a paginated(page, limit) -> Vec<&Task> helper.
• tests/integration.rs — at least three new tests.

Suggested commit shape

• feat: add ?page= and ?limit= pagination to GET /tasks
• test: cover default, second, partial, and out-of-range pages
• fix: reject page=0 and limit=0 with 400 Bad Request

Verification

• cargo test — all tests pass.
• cargo fmt --check && cargo clippy --all-targets -- -D warnings — clean.

See docs/issues/03-add-pagination.md for the full spec.