Fix Docker build error; add multi-year view, PDF export, ntfy notifier

Fix: remove unused 'accessibleMonths' variable (tsc exit code 2)

Features:
- AllYearsLetter view: all years in chronological order, reachable
  from "All Years" at the top of the sidebar
- PDF export: window.print() with @media print CSS — sidebar, toolbar,
  and chrome hidden; each year starts on a new page via page-break
- "Download all" exports a plain-text file of every year's letter
- ntfy notifier: standalone Node.js service (notifier/) that fires a
  push notification via ntfy on the 1st of each month; configurable
  via NTFY_TOPIC, NTFY_URL, CRON_SCHEDULE, APP_URL env vars
- docker-compose: adds `notifier` service alongside `app`; reads from
  .env (example in .env.example); NTFY_TEST_ON_START=true sends a
  test ping on container start

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -6,6 +6,7 @@ import { LetterView } from "./components/LetterView";
 import { Welcome } from "./components/Welcome";
 import { PodcastYearEndForm } from "./components/PodcastYearEnd";
 import { Home } from "./components/Home";
+import { AllYearsLetter } from "./components/AllYearsLetter";
 import {
   load,
   save,
@@ -100,6 +101,9 @@ export default function App() {
         {view.kind === "letter" && (
           <LetterView data={data} year={view.year} />
         )}
+        {view.kind === "allYears" && (
+          <AllYearsLetter data={data} />
+        )}
         {view.kind === "podcast" && (
           <PodcastYearEndForm
             key={view.year}