fix(dashboard): restore shift-click suggestion submit

Default domain was retired slug "custodian", so POST /technical-debt/
returned 422 and the modal failed after open. Use infotech, resolve
apiBase like config.js, and surface API error detail in the toast.

dashboard/test/improvement-modal.test.mjs

@@ -0,0 +1,46 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import {readFileSync} from "node:fs";
+import {dirname, join} from "node:path";
+import {fileURLToPath} from "node:url";
+
+import {
+  DEFAULT_IMPROVEMENT_DOMAIN,
+  resolveImprovementApiBase,
+} from "../src/components/improvement-modal.js";
+
+const root = dirname(fileURLToPath(import.meta.url));
+const modalSource = readFileSync(
+  join(root, "../src/components/improvement-modal.js"),
+  "utf-8",
+);
+
+test("dashboard-improvement default domain is the live infotech slug", () => {
+  assert.equal(DEFAULT_IMPROVEMENT_DOMAIN, "infotech");
+  // Regression: custodian was retired from the domain registry; POST /technical-debt/
+  // returns 422 for unknown domain, so the shift-wait-click modal must not use it.
+  assert.doesNotMatch(modalSource, /domain\s*=\s*["']custodian["']/);
+  assert.match(modalSource, /domain\s*=\s*DEFAULT_IMPROVEMENT_DOMAIN/);
+  assert.match(modalSource, /debt_type:\s*["']dashboard-improvement["']/);
+});
+
+test("improvement modal api base mirrors dashboard config resolution", () => {
+  assert.equal(
+    resolveImprovementApiBase({location: null, storage: null}),
+    "http://127.0.0.1:8000",
+  );
+  assert.equal(
+    resolveImprovementApiBase({
+      location: new URL("http://localhost:3000/workstreams"),
+      storage: null,
+    }),
+    "http://localhost:8000",
+  );
+  assert.equal(
+    resolveImprovementApiBase({
+      location: new URL("http://localhost:3000/?api_base=http%3A%2F%2F127.0.0.1%3A18000%2F"),
+      storage: {getItem: () => "http://ignored.example:8000"},
+    }),
+    "http://127.0.0.1:18000",
+  );
+});