Remove federation functionality and related tests

- Deleted the `federation.rs` module and its associated functionality for federating thoughts to followers.
- Removed the `well_known.rs` module and its WebFinger discovery functionality.
- Eliminated references to federation in the `thought.rs` router and removed the spawning of background tasks for federating thoughts.
- Deleted tests related to WebFinger and user inbox interactions in `activitypub.rs`.
- Updated `Cargo.toml` to remove the `activitypub_federation` dependency.

thoughts-backend/api/Cargo.toml

@@ -38,6 +38,5 @@ tower-http = { version = "0.6.6", features = ["fs", "cors"] }
 tower-cookies = "0.11.0"
 anyhow = "1.0.98"
 dotenvy = "0.15.7"
-activitypub_federation = "0.6.5"
-url = "2.5.7"
+
 [dev-dependencies]