feat: pairing v2 — one-tap trusted devices over LAN and private relay (#2103)

Reworks how devices connect to an OpenChamber server, end to end.

Pairing v2:
- One-time pairing links/QR codes (openchamber://connect?v=2) carrying a set of transport candidates (LAN/tunnel/relay) and a single-use secret redeemed server-side; no tokens embedded in links
- Add-a-device dialog written for first-time users: intent-based transport choice (Anywhere / Home network only / This computer only) with plain-language descriptions, transparent fallback checkboxes, server-authoritative LAN detection, high-res QR dialog
- Private relay folded into pairing as a transport candidate with a demand-driven lifecycle (enables when a relay device is paired, disables when none remain)

Multi-transport devices:
- A saved device holds all its transports and one token; mobile re-probes on connect, resume, and network change and hot-switches LAN<->relay seamlessly (no re-pairing, no remount, session preserved)
- Desktop can import relay pairing links, switch to relay hosts through the E2EE tunnel, and restore a relay default host after relaunch

Device management:
- Device list (web + desktop) shows live per-device connectivity with the active transport (Connected - Local network / Relay) and platform badges (iOS/Android/macOS/Windows/Linux)
- One physical device = one record: stable per-install dedupe keys across pairing and password re-login; typed pairing label names the device, paired devices name the connection by the issuing server hostname
- Trusted desktop-local client manages all devices (list, revoke, clear revoked); relay host reaps dead client sockets after 3 missed keepalives

Android:
- LAN transport unblocked (cleartext + mixed content, mirroring iOS ATS exceptions); resume re-probe retries through network flux and silently auto-reconnects from a disconnected state

packages/ui/src/sync/use-sync.ts

@@ -349,7 +349,14 @@ export function useSync() {
       setMetaFor(sessionID, { loading: true })
 
       try {
-        const limit = options?.before ? HISTORY_MESSAGE_PAGE_SIZE : m.limit
+        // A resync (no `before`) must fetch at least as many messages as we
+        // already have on screen. Live events append to the store WITHOUT growing
+        // m.limit, so reusing the stale m.limit here would under-fetch and make
+        // the server hand back a spurious "older" cursor — surfacing a phantom
+        // "load older" button for a session whose full history is already shown
+        // (e.g. after a reconnect resync following a few new messages).
+        const storeMessageCount = store.getState().message[sessionID]?.length ?? 0
+        const limit = options?.before ? HISTORY_MESSAGE_PAGE_SIZE : Math.max(m.limit, storeMessageCount)
         let page = await fetchMessages(sessionID, limit, options?.before)
 
         // Keep the initial page small for switch performance. Some sessions