Rename the crate from invoiceninjars to invoiceninja-sdk

The package name has never matched the repository it lives in
(gitea.awkawb.cloud/awkawb/invoiceninja-sdk, mirrored to
github.com/awkawb1/invoiceninja-sdk) — both pointed at `invoiceninja-sdk`
while `Cargo.toml` declared `invoiceninjars`. Lines everything up on the
name the repo has always used.

Cargo derives the crate's Rust identifier from the package name by
lowercasing hyphens to underscores, so every `use invoiceninjars::...`
becomes `use invoiceninja_sdk::...` — in doctests across `src/`, the four
examples, all four integration test files, and `README.md`. `Cargo.lock`'s
own self-entry picked up the new name on the next `cargo check`, which is
also when the rename gets its real check: every doctest and every test file
has to resolve the new path to compile at all, not just the ones a grep
happens to catch.

`flake.nix`'s `pname` and description follow, so `nix build` produces
`invoiceninja-sdk-0.1.0.drv` rather than a name that no longer matches
anything. `GOALS.md`'s two mentions — the hypothetical CLI's name and the
`cargo install` example — follow too, for the same reason.

Verified clean on both the dev toolchain and the 1.88 MSRV shell: full test
suite (209 tests), clippy, fmt, and `nix build`/`nix flake check`.

Not yet published to crates.io (checked: the name 404s there), so this
lands before the old name was ever claimed — no one's `Cargo.toml` breaks
today, but it's recorded as a Changed entry since `GOALS.md` asks for
breaking changes to be legible in the changelog rather than discovered at
compile time, and the crate is reachable as a git dependency regardless of
crates.io status.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/client_requests.rs

@@ -8,7 +8,7 @@
 
 use std::time::Duration;
 
-use invoiceninjars::{models::ListParams, Error, InvoiceNinjaClient};
+use invoiceninja_sdk::{models::ListParams, Error, InvoiceNinjaClient};
 use serde_json::json;
 use wiremock::matchers::{header, method, path, query_param};
 use wiremock::{Mock, MockServer, ResponseTemplate};
@@ -547,7 +547,7 @@ async fn ping_accepts_an_empty_success_body() {
 
 // --- retry and backoff --------------------------------------------------
 
-use invoiceninjars::RetryPolicy;
+use invoiceninja_sdk::RetryPolicy;
 
 /// Fast policy so the tests do not actually sleep for seconds.
 fn quick_retry() -> RetryPolicy {
@@ -751,7 +751,7 @@ async fn retried_requests_keep_their_body_and_headers() {
         .mount(&server)
         .await;
 
-    let body = invoiceninjars::models::Client {
+    let body = invoiceninja_sdk::models::Client {
         name: "Acme".into(),
         ..Default::default()
     };
@@ -965,7 +965,7 @@ async fn send_email_unwraps_the_data_envelope() {
         .mount(&server)
         .await;
 
-    let invoice: invoiceninjars::models::Invoice = client(&server)
+    let invoice: invoiceninja_sdk::models::Invoice = client(&server)
         .send_email(&json!({ "entity": "invoice", "entity_id": "inv1" }))
         .await
         .expect("should return the refreshed entity");
@@ -1179,7 +1179,7 @@ async fn no_budget_means_only_max_retries_bounds_the_call() {
 
 // --- document uploads ---------------------------------------------------
 
-use invoiceninjars::FileUpload;
+use invoiceninja_sdk::FileUpload;
 
 fn pdf(name: &str) -> FileUpload {
     FileUpload::new(name, b"%PDF-1.4 fake".to_vec()).mime("application/pdf")