refactor(domain): add FeedId, EmailAddress and Domain value objects

Encapsulate the email/domain/feed-id parsing that was scattered as ad-hoc
regexes and split("@") calls into three small immutable value objects under
src/domain/value-objects/. EmailParser.extractFeedId and generateFeedId now
delegate to FeedId; the sender policy, favicon domain extraction and the admin
SenderField parse through EmailAddress/Domain.

Left as-is on purpose: forwardemail's multi-address free-text extraction and the
admin allow/block list normaliser, which operate on mixed email-or-domain input
that the single-address value objects would reject.

Behaviour-preserving; adds unit tests for each value object.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/domain/value-objects/domain.test.ts

@@ -0,0 +1,25 @@
+import { describe, it, expect } from "vitest";
+import { Domain } from "./domain";
+
+describe("Domain", () => {
+  it("normalises case and whitespace", () => {
+    expect(Domain.parse("  Example.COM ")?.value).toBe("example.com");
+  });
+
+  it("strips a leading @ and trailing dots", () => {
+    expect(Domain.parse("@example.com")?.value).toBe("example.com");
+    expect(Domain.parse("example.com.")?.value).toBe("example.com");
+  });
+
+  it("returns null for empty input", () => {
+    expect(Domain.parse("")).toBeNull();
+    expect(Domain.parse("@")).toBeNull();
+  });
+
+  it("compares by normalised value", () => {
+    expect(
+      Domain.parse("Example.com")!.matches(Domain.parse("example.com")!),
+    ).toBe(true);
+    expect(Domain.parse("a.com")!.matches(Domain.parse("b.com")!)).toBe(false);
+  });
+});