Localization (#1)

Implement comprehensive content localization, admin panels for editing each language, AI translation interface with automatic updates when base language version is changed.
- SEO tags for all language URLs
- Uses accept-language by default, ?lang=en overrides temporarily
- User edits patched on top of translations
- RTL language supportReviewed-on: #1

frontend/src/reconnect.js

@@ -0,0 +1,56 @@
+// Shared reconnect policy for the WebSockets (page/banner editors,
+// analytics view, the activity channel). Two things trip a browser's
+// WebSocket throttling, after which every socket to the host sits
+// "pending" (never opens, never closes) for minutes:
+//
+//  1. A burst of simultaneous attempts — page load opens Vite's HMR
+//     socket plus several of ours at the same moment, and every refresh
+//     repeats the burst. socketSlot() spaces new sockets out.
+//  2. Too-frequent retries — so failed attempts back off exponentially
+//     (a few seconds, doubling to half a minute), reset only after a
+//     connection stayed open long enough to count as healthy. A socket
+//     that closes right after opening must NOT reset the backoff.
+export function reconnectPolicy({ min = 2000, max = 30000, healthyAfter = 30000 } = {}) {
+  let delay = min
+  let openedAt = 0
+  return {
+    // Stamp a socket that just opened.
+    opened() {
+      openedAt = Date.now()
+    },
+    // The socket closed: the wait before the next attempt (up to 50%
+    // jitter; the base doubles per failure). A healthy streak resets it.
+    closed() {
+      if (openedAt && Date.now() - openedAt >= healthyAfter) delay = min
+      openedAt = 0
+      const wait = Math.round(delay * (1 + Math.random() * 0.5))
+      delay = Math.min(delay * 2, max)
+      return wait
+    },
+  }
+}
+
+// Sockets created at the same moment (page load: Vite's HMR socket plus
+// ours) read as one burst to the browser's throttling. Space new sockets
+// out: each call reserves a slot a beat after the previous one.
+let nextSlot = 0
+export function socketSlot() {
+  const now = Date.now()
+  const wait = Math.max(0, nextSlot - now)
+  nextSlot = Math.max(now, nextSlot) + 300
+  return wait
+}
+
+// A socket still CONNECTING after this long counts as a failed attempt:
+// browser throttling leaves sockets "pending" (no open, no close) for
+// minutes, and without a watchdog the app would wait on one forever (the
+// recurring empty editor). Closing it fires onclose, which reschedules
+// through the policy's backoff — it never reconnects aggressively itself.
+export function watchConnecting(ws, label) {
+  return setTimeout(() => {
+    if (ws.readyState === WebSocket.CONNECTING) {
+      console.warn(`[pagerite] ${label} socket stuck connecting — closing it, retrying with backoff`)
+      ws.close()
+    }
+  }, 10_000)
+}