Add Klipper, OctoPrint and PrusaLink printers from the API

POST /farms/:id/printers now takes any of the four vendors the gateway can
drive. Credentials depend on the vendor: Bambu needs an access code and
serial, OctoPrint and PrusaLink an API key, Klipper nothing. A missing one
is a 422 naming what is needed. The API key is relayed to the gateway and
kept out of logs and errors like the access code.

The printer_vendor enum gains octoprint (migration 0006); PrusaLink is
stored as prusa, the name the enum already had.

scripts/e2e-vendors.sh adds each kind through the API against a fake REST
printer (scripts/fake-http-printer.ts) and runs a job through the real
scheduler to completion. The fake shares its author's reading of the docs
with the driver, so this proves the plumbing, not the protocols.

tests/provision.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "bun:test";
-import { gatewayIdFor, safeGatewayError } from "../src/provision/plan";
+import { dbVendorFor, gatewayIdFor, missingCredential, safeGatewayError } from "../src/provision/plan";
 
 describe("gatewayIdFor", () => {
   const accepted = /^[A-Za-z0-9_-]{1,64}$/;
@@ -38,3 +38,21 @@ describe("safeGatewayError", () => {
     expect(safeGatewayError(undefined, [])).toBe("the gateway did not say why");
   });
 });
+
+describe("missingCredential", () => {
+  test("a Bambu needs its access code and serial number", () => {
+    expect(missingCredential("bambu", {})).toBe("an access code");
+    expect(missingCredential("bambu", { accessCode: "12345678" })).toBe("a serial number");
+    expect(missingCredential("bambu", { accessCode: "12345678", serialNumber: "01P00A123" })).toBeUndefined();
+  });
+  test("OctoPrint and PrusaLink need an API key; Klipper needs nothing", () => {
+    expect(missingCredential("octoprint", { accessCode: "x" })).toBe("an API key");
+    expect(missingCredential("prusa_link", { apiKey: "  " })).toBe("an API key");
+    expect(missingCredential("prusa_link", { apiKey: "k" })).toBeUndefined();
+    expect(missingCredential("klipper", {})).toBeUndefined();
+  });
+  test("the gateway's PrusaLink is stored under the database's older name", () => {
+    expect(dbVendorFor("prusa_link")).toBe("prusa");
+    expect(dbVendorFor("octoprint")).toBe("octoprint");
+  });
+});