P1 complete: web front, test suite, CI — acceptance ALL GREEN

Fan-out integration + fixes found by the test/acceptance pass:
- FIX ring-buffer: chunks >= capacity skipped bytes now count into the
  monotonic offset (invariant: stream byte k lives at k % capacity) —
  window order was corrupted on unaligned big chunks
- FIX auth: non-numeric cookie expiry no longer bypasses expiration
- FIX protocol: safe-integer validation on ack.bytes / hello.protocol
- FIX @fastify/websocket v11: websocket route must be registered in an
  encapsulated context after plugin load (handler got REST signature)
- FIX flow-control deadlock found by e2e acceptance: client only ACKs
  on data receipt, so pausing with an unACKed residue in (LOW,
  ACK_EVERY] stalled both sides at 0.9 MB. ACK_EVERY now 64 KiB (<=
  LOW invariant, tested) + trailing debounced ACK in the web client
- Web: Vue 3 + Vite + Pinia + Tailwind 4 + vue-i18n (EN/FR) + xterm 6
  (fit + webgl fallback), multiplexed ws-client with reconnect/backoff
  and resync epochs
- Tests: 100 vitest (protocol fuzz, ring edges, auth, pty-manager flow
  control with mocked pty, REST e2e) ; CI Node 22/24 + pack-smoke
- scripts/acceptance-p1.mjs: real daemon + real WS client — boot,
  login, attach, stdin, 10 MB flood w/ ACK (13.7 MB/1.9s, RSS bounded),
  brutal disconnect + replay resync, kill broadcast, SIGTERM drain

packages/web/src/i18n/en.ts

@@ -0,0 +1,49 @@
+export default {
+  common: {
+    appName: 'Arboretum',
+    loading: 'Loading…',
+    cancel: 'Cancel',
+    logout: 'Log out',
+    language: 'Language',
+  },
+  login: {
+    title: 'Sign in with your access token',
+    tokenLabel: 'Access token',
+    tokenPlaceholder: 'arb_…',
+    submit: 'Sign in',
+    submitting: 'Signing in…',
+    invalidToken: 'Invalid token',
+    rateLimited: 'Too many attempts — please wait before retrying',
+    genericError: 'Sign-in failed ({status})',
+  },
+  sessions: {
+    title: 'Sessions',
+    refresh: 'Refresh',
+    empty: 'No sessions yet — start one below.',
+    newSession: 'New session',
+    cwdLabel: 'Working directory',
+    cwdPlaceholder: '/absolute/path/to/project',
+    commandLabel: 'Command',
+    creating: 'Creating…',
+    open: 'Open',
+    observe: 'Observe',
+    kill: 'Kill',
+    confirmKill: 'Confirm kill',
+    live: 'live',
+    clients: 'no client | 1 client | {n} clients',
+    exitCode: 'exit code {code}',
+    statusLabel: {
+      starting: 'starting',
+      running: 'running',
+      exited: 'exited',
+    },
+  },
+  terminal: {
+    observer: 'observer (read-only)',
+    sessionEnded: 'Session ended',
+    back: 'Sessions',
+  },
+  ws: {
+    reconnecting: 'Connection lost — reconnecting…',
+  },
+};