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/components/Sidebar.tsx

@@ -6,7 +6,8 @@ export type View =
   | { kind: "month"; year: number; month: number }
   | { kind: "yearEnd"; year: number }
   | { kind: "letter"; year: number }
-  | { kind: "podcast"; year: number };
+  | { kind: "podcast"; year: number }
+  | { kind: "allYears" };
 
 interface SidebarProps {
   data: AppData;
@@ -36,6 +37,17 @@ export function Sidebar({
         <span className="brand-name">Annual Letter</span>
       </button>
 
+      <ul className="sidebar-months" style={{ marginBottom: 8 }}>
+        <li>
+          <button
+            className={`sidebar-item sidebar-letter ${view.kind === "allYears" ? "active" : ""}`}
+            onClick={() => onViewChange({ kind: "allYears" })}
+          >
+            <span className="sidebar-item-name">📚 All Years</span>
+          </button>
+        </li>
+      </ul>
+
       {years.map((year) => {
         const monthEntries = data.monthlyEntries.filter((e) => e.year === year);
         const yearEndEntry = data.yearEndEntries.find((e) => e.year === year);