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/index.css

@@ -377,6 +377,56 @@ body { font-family: "Georgia", serif; background: var(--bg); color: var(--text);
   padding: 12px 0;
 }
 
+/* ─── All-years view ─────────────────────────────────────────────────────── */
+.all-years-content { display: flex; flex-direction: column; gap: 0; }
+.year-letter-block { }
+.year-divider { border: none; border-top: 2px dashed var(--border); margin: 48px 0; }
+
+/* ─── Print / PDF export ─────────────────────────────────────────────────── */
+@media print {
+  /* Hide everything except the letter content */
+  .sidebar,
+  .letter-toolbar,
+  .toolbar-actions,
+  .home-header button,
+  .tab-bar {
+    display: none !important;
+  }
+
+  .layout {
+    display: block;
+  }
+
+  .main {
+    padding: 0;
+    max-width: 100%;
+  }
+
+  .letter-content,
+  .all-years-content .letter-content {
+    border: none;
+    box-shadow: none;
+    padding: 0;
+    max-width: 100%;
+    font-size: 11pt;
+    line-height: 1.7;
+  }
+
+  .year-divider {
+    border-top: 1px solid #999;
+    margin: 32pt 0;
+  }
+
+  /* Each year starts on a new page */
+  .print-page-break + .print-page-break {
+    page-break-before: always;
+  }
+
+  @page {
+    margin: 1.2in 1in;
+  }
+}
+
 /* ─── Tabs ───────────────────────────────────────────────────────────────── */
 .tab-bar {
   display: flex;