✨ Fix issue #24: Use GitHub GraphQL API instead of REST API

[nicokosi]

Via Junie, using issue's description as agent prompt.

[nicokosi]

It compiles, but... 😇

 RUST_LOG=pullpito=debug cargo run -- --repository nicokosi/pullpito
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.11s
     Running `target/debug/pullpito --repository nicokosi/pullpito`
[2025-06-23T15:59:48Z INFO  pullpito] Computing stats for GitHub repos '["nicokosi/pullpito"]' (with token: false)
[2025-06-23T15:59:48Z DEBUG pullpito] Query stats for GitHub repo "nicokosi/pullpito"
[2025-06-23T15:59:48Z DEBUG pullpito::github_events] No token provided for GraphQL API, which may result in rate limiting
[2025-06-23T15:59:48Z DEBUG pullpito::github_events] Content found for "nicokosi/pullpito"
[2025-06-23T15:59:48Z DEBUG pullpito::github_events] No data in GraphQL response

thread '<unnamed>' panicked at src/lib.rs:83:88:
called `Result::unwrap()` on an `Err` value: Custom { kind: Other, error: "No data in GraphQL response" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[nicokosi]

I'll maybe try another time... or not! 😇