Add logout, passkey management, and a standalone login

The "auth routes" open question in GOALS.md conflated four unrelated
things once the upstream routes and controllers were checked: logout and
the passkey settings routes sit behind the same token_auth middleware as
everything else this crate wraps, login needs a credential exchange since
there's no token yet, refresh/refresh_react turned out to be the bulk
sync-dump endpoint already parked as a separate open question, and
connected_account is Gmail OAuth linking that belongs with Integrations.

Adds logout, list_passkeys, delete_passkey (passkey registration is left
out — it needs a WebAuthn ceremony a browser has to drive), and
InvoiceNinjaClient::login as an associated function returning a lean
LoginResponse that types only is_owner/is_admin/token and leaves the
server's much larger nested payload in extra.

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

src/models/login.rs

@@ -0,0 +1,34 @@
+use serde::{Deserialize, Serialize};
+use serde_json::{Map, Value};
+
+use super::CompanyToken;
+
+/// Response of `POST /login` (via [`crate::InvoiceNinjaClient::login`]).
+///
+/// One entry per company the account can access. The full upstream payload
+/// also nests the whole company (clients, invoices, designs, ...), the
+/// user, and the account under each entry — this crate does not model that;
+/// it stays reachable, losslessly, through [`LoginCompanyUser::extra`].
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct LoginResponse {
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub data: Vec<LoginCompanyUser>,
+}
+
+/// One company membership returned by a login, carrying that company's API
+/// token.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct LoginCompanyUser {
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub is_owner: bool,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub is_admin: bool,
+    /// The token to pass to [`InvoiceNinjaClient::new`](crate::InvoiceNinjaClient::new)
+    /// for this company. Only absent if the server ever omits the `token`
+    /// include; every server-side `first_load` request requests it.
+    #[serde(default)]
+    pub token: Option<CompanyToken>,
+
+    #[serde(flatten)]
+    pub extra: Map<String, Value>,
+}