Add invoices, quotes, payments, products, and expenses

Five more resources following clients.rs's template exactly: the
same list/get/create/update/delete shape, including the
fetch-merge-write pattern for update. quotes.rs is otherwise
identical to invoices.rs since Quote is a type alias for Invoice in
the SDK (same table, distinguished by entity_type upstream).

Verified against a live local server: full create/list/get/update/
delete round trip for all six resources, confirming update preserves
fields the caller didn't mention.

Also adds CHANGELOG.md (Keep a Changelog format, matching the SDK's)
and updates README/CLAUDE.md's resource counts.

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

README.md

@@ -3,9 +3,10 @@
 A command-line client for the [Invoice Ninja](https://www.invoiceninja.com/)
 v5 API, built on [`invoiceninja-sdk`](https://crates.io/crates/invoiceninja-sdk).
 
-> **Early scaffold.** Only the `clients` resource is wired up so far, as the
-> template for adding the rest — see `CLAUDE.md` for the pattern.
-> [`GOALS.md`](GOALS.md) covers what the crate is for and what it is not.
+> **Early scaffold.** `clients`, `invoices`, `quotes`, `payments`, `products`,
+> and `expenses` are wired up so far, out of ~34 resources — see `CLAUDE.md`
+> for the pattern the rest follow. [`GOALS.md`](GOALS.md) covers what the
+> crate is for and what it is not.
 
 ## Development
 
@@ -46,3 +47,8 @@ table view's few key columns:
 ```sh
 invoiceninja-cli --output json clients get <id>
 ```
+
+Every other wired-up resource (`invoices`, `quotes`, `payments`, `products`,
+`expenses`) follows the same `list`/`get`/`create`/`update`/`delete` shape,
+e.g. `invoiceninja-cli invoices list --status active` or
+`invoiceninja-cli payments get <id>`.