Add credits, projects, tasks, vendors, and purchase orders

Five more resources following clients.rs's template exactly, same as
the previous batch. credits.rs is otherwise identical to quotes.rs
since Credit is also 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 five.

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

src/commands/purchase_orders.rs

@@ -0,0 +1,141 @@
+//! `purchase-orders` subcommand. Same shape as `clients.rs` — see the
+//! "Adding a resource" section in CLAUDE.md.
+
+use invoiceninja_sdk::models::{ListParams, PurchaseOrder};
+use invoiceninja_sdk::InvoiceNinjaClient;
+
+use crate::body;
+use crate::cli::{Action, BodyArgs, ListArgs, OutputFormat, ResourceArgs};
+use crate::output;
+
+pub async fn run(
+    client: &InvoiceNinjaClient,
+    args: ResourceArgs,
+    format: OutputFormat,
+) -> Result<(), Box<dyn std::error::Error>> {
+    match args.action {
+        Action::List(list_args) => list(client, list_args, format).await,
+        Action::Get { id } => get(client, &id, format).await,
+        Action::Create(body_args) => create(client, body_args, format).await,
+        Action::Update { id, body } => update(client, &id, body, format).await,
+        Action::Delete { id } => delete(client, &id).await,
+    }
+}
+
+async fn list(
+    client: &InvoiceNinjaClient,
+    args: ListArgs,
+    format: OutputFormat,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let mut params = ListParams::new();
+    if let Some(page) = args.page {
+        params = params.page(page);
+    }
+    if let Some(per_page) = args.per_page {
+        params = params.per_page(per_page);
+    }
+    if let Some(sort) = args.sort {
+        params = params.sort(sort);
+    }
+    if let Some(filter) = args.filter {
+        params = params.filter(filter);
+    }
+    if let Some(status) = args.status {
+        params = params.status(status);
+    }
+    if let Some(include) = args.include {
+        params = params.include(include);
+    }
+    for (k, v) in args.params {
+        params = params.param(k, v);
+    }
+
+    let purchase_orders = if args.all {
+        client.list_all_purchase_orders(&params).await?
+    } else {
+        client.list_purchase_orders(&params).await?
+    };
+
+    render(&purchase_orders, format)
+}
+
+async fn get(
+    client: &InvoiceNinjaClient,
+    id: &str,
+    format: OutputFormat,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let found = client.get_purchase_order(id).await?;
+    render(std::slice::from_ref(&found), format)
+}
+
+async fn create(
+    client: &InvoiceNinjaClient,
+    body_args: BodyArgs,
+    format: OutputFormat,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let value = body::load(&body_args)?;
+    let model: PurchaseOrder = serde_json::from_value(value)?;
+    let created = client.create_purchase_order(&model).await?;
+    render(std::slice::from_ref(&created), format)
+}
+
+async fn update(
+    client: &InvoiceNinjaClient,
+    id: &str,
+    body_args: BodyArgs,
+    format: OutputFormat,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let patch = body::load(&body_args)?;
+    let current = client.get_purchase_order(id).await?;
+    let merged = body::merge_shallow(serde_json::to_value(&current)?, patch);
+    let model: PurchaseOrder = serde_json::from_value(merged)?;
+    let updated = client.update_purchase_order(id, &model).await?;
+    render(std::slice::from_ref(&updated), format)
+}
+
+async fn delete(client: &InvoiceNinjaClient, id: &str) -> Result<(), Box<dyn std::error::Error>> {
+    client.delete_purchase_order(id).await?;
+    println!("deleted {id}");
+    Ok(())
+}
+
+fn render(
+    purchase_orders: &[PurchaseOrder],
+    format: OutputFormat,
+) -> Result<(), Box<dyn std::error::Error>> {
+    match format {
+        OutputFormat::Json => output::print_json(purchase_orders)?,
+        OutputFormat::Table => print_table(purchase_orders),
+    }
+    Ok(())
+}
+
+fn print_table(purchase_orders: &[PurchaseOrder]) {
+    if purchase_orders.is_empty() {
+        println!("(no records)");
+        return;
+    }
+    println!(
+        "{:<20}  {:<15}  {:<20}  {:<8}  {:>12}  {:>12}",
+        "id", "number", "vendor_id", "status", "amount", "balance"
+    );
+    for po in purchase_orders {
+        println!(
+            "{:<20}  {:<15}  {:<20}  {:<8}  {:>12.2}  {:>12.2}",
+            po.id.as_deref().unwrap_or(""),
+            truncate(&po.number, 15),
+            truncate(&po.vendor_id, 20),
+            po.status_id,
+            po.amount,
+            po.balance
+        );
+    }
+}
+
+fn truncate(s: &str, max: usize) -> String {
+    if s.chars().count() <= max {
+        s.to_string()
+    } else {
+        s.chars().take(max.saturating_sub(1)).collect::<String>() + "…"
+    }
+}