feat: reader-rendering correctness + privacy hardening (P1·S batch)

Close the five open P1·S items from TODO.md:
- X-Robots-Tag: noindex on rss/atom/entries/files + a /robots.txt
- absolutize relative content URLs against the sender's site
- promote lazy-loaded images (data-src → src, strip loading="lazy")
- strip XML-illegal control chars from generated feeds (keep emoji)
- plain-text feed <title> (strip HTML, decode entities)

Sender-base derivation lives on the EmailAddress value object
(siteBaseUrl) instead of a misplaced favicon helper. Bump to 0.2.1
and document the changes in README + CLAUDE.md.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/routes/rss.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { Hono } from "hono";
+import { handle } from "./rss";
+import { createMockEnv } from "../test/setup";
+import { Env } from "../types";
+
+describe("RSS Feed Route", () => {
+  let testApp: Hono;
+  let mockEnv: Env;
+
+  beforeEach(() => {
+    mockEnv = createMockEnv() as unknown as Env;
+    testApp = new Hono();
+    testApp.get("/:feedId", handle);
+  });
+
+  describe("unknown feed", () => {
+    it("returns 404 when no metadata exists in KV", async () => {
+      const res = await testApp.request("/nonexistent-feed", {}, mockEnv);
+      expect(res.status).toBe(404);
+      expect(await res.text()).toBe("Feed not found");
+    });
+  });
+
+  describe("valid feed with no emails", () => {
+    beforeEach(async () => {
+      await mockEnv.EMAIL_STORAGE.put(
+        "feed:empty-feed:metadata",
+        JSON.stringify({ emails: [] }),
+      );
+    });
+
+    it("returns 200 with application/rss+xml content type", async () => {
+      const res = await testApp.request("/empty-feed", {}, mockEnv);
+      expect(res.status).toBe(200);
+      expect(res.headers.get("Content-Type")).toContain("application/rss+xml");
+    });
+
+    it("includes Cache-Control header", async () => {
+      const res = await testApp.request("/empty-feed", {}, mockEnv);
+      expect(res.headers.get("Cache-Control")).toBe("max-age=1800");
+    });
+
+    it("sets X-Robots-Tag: noindex", async () => {
+      const res = await testApp.request("/empty-feed", {}, mockEnv);
+      expect(res.headers.get("X-Robots-Tag")).toBe("noindex");
+    });
+
+    it("Link header advertises hub and self for WebSub discovery", async () => {
+      const res = await testApp.request("/empty-feed", {}, mockEnv);
+      const link = res.headers.get("Link") ?? "";
+      expect(link).toContain(`rel="hub"`);
+      expect(link).toContain(`rel="self"`);
+    });
+  });
+});