fix: apply security and correctness review findings across both stacks

Legacy panel:
- upstream body reads now carry their own deadline and a 10 MB byte budget;
  a stalled modem can no longer hang /api/status fan-out forever nor OOM
  the proxy (request headers alone had the timeout, bodies had none)
- add X-Frame-Options DENY / CSP frame-ancestors none / nosniff; the panel
  (delete-instance and confirmed-write dialogs) is no longer clickjackable
- only send a JSON content-type when the API console request has a body, so
  payload-less dangerous writes stop failing with 400 and burning the
  one-use confirmation token
- register a form-urlencoded parser (the proxy branch was unreachable) and
  drop the multipart parser that buffered up to 60 MB before rejecting;
  bodyLimit drops to 2 MB; framework-level 415 keeps the stable error body
- remove /api/sms/send from readable paths: GET bypassed the write
  confirmation for a send endpoint
- /api/instances/:id/login maps upstream failures to a stable 502 instead
  of leaking raw error text
- guard MULTI_SIMADMIN_TIMEOUT_MS parsing (NaN aborted every request);
  prune dead code (buildClients, cookie expando no-op)

Control plane:
- deleting a notification channel detaches it from rules instead of leaving
  dangling ids that made every referencing rule unreadable and silently
  dropped future notifications; rule reads tolerate unknown ids
- startup sweep resets notification_queue rows stranded in 'sending' by a
  crash (mirrors the sms outbox sweep); terminal outbox rows are pruned on
  the retention timer
- /api/v1/metrics no longer emits operator-assigned node names on the
  session-free scrape; login limiter map is bounded and pruned; Secure
  cookie honors the gateway-declared x-forwarded-proto
- webhook delivery sets redirect: manual (signed payloads are not replayed)
- SMTP envelope sender is validated against CR/LF smuggling
- scheduled reboots with delaySeconds != 3 fail fast at the dispatcher with
  a clear reason instead of burning every retry; contract narrowed to the
  pinned baseline

server/app.js

@@ -24,7 +24,7 @@ const CATALOG = [
 
 export async function buildApp({ configStore, clientRegistry, logger = false, staticFiles = true, publicDir = path.join(ROOT, 'public'), reconcileRetryMs = 100, proxyPolicy = defaultProxyPolicy, confirmationOptions = {} } = {}) {
   if (!configStore || !clientRegistry) throw new TypeError('configStore and clientRegistry are required')
-  const app = Fastify({ logger, bodyLimit: 60 * 1024 * 1024 })
+  const app = Fastify({ logger, bodyLimit: 2 * 1024 * 1024 })
   const parseAuthority = raw => {
     const value = String(raw || '').trim().toLowerCase()
     if (!value || /[\s/@]/.test(value)) return null
@@ -46,6 +46,11 @@ export async function buildApp({ configStore, clientRegistry, logger = false, st
   const configuredRawHost = String(configStore.snapshot.server.host).replace(/^\[|\]$/g, '').toLowerCase()
   const configuredHost = isIP(configuredRawHost) === 6 ? '::1' : configuredRawHost
   const configuredPort = String(configStore.snapshot.server.port)
+  app.addHook('onRequest', async (_request, reply) => {
+    reply.header('x-frame-options', 'DENY')
+    reply.header('content-security-policy', "frame-ancestors 'none'")
+    reply.header('x-content-type-options', 'nosniff')
+  })
   app.addHook('onRequest', async (request, reply) => {
     const authority=loopbackAuthority(request.headers.host)
     const injectDefault = request.headers.host === 'localhost:80' && request.raw.socket?.localPort == null
@@ -58,7 +63,14 @@ export async function buildApp({ configStore, clientRegistry, logger = false, st
     }
   })
   app.addContentTypeParser('application/octet-stream', { parseAs: 'buffer' }, (_request, body, done) => done(null, body))
-  app.addContentTypeParser(/^multipart\//, { parseAs: 'buffer' }, (_request, body, done) => done(null, body))
+  app.addContentTypeParser('application/x-www-form-urlencoded', { parseAs: 'string' }, (_request, body, done) => done(null, body))
+  // Unparsable content types (e.g. multipart) must fail with the same stable body
+  // the proxy policy would have produced, without buffering the payload first.
+  app.setErrorHandler((error, _request, reply) => {
+    if (error?.code === 'FST_ERR_CTP_INVALID_MEDIA_TYPE') return reply.code(415).send({ error: 'unsupported proxy content type' })
+    if (error?.code === 'FST_ERR_CTP_EMPTY_JSON_BODY') return reply.code(400).send({ error: 'empty JSON body' })
+    reply.send(error)
+  })
   if (staticFiles) await app.register(fastifyStatic, { root: publicDir, prefix: '/' })
   const findClient = (id, reply) => {
     const client = clientRegistry.get(id)
@@ -101,7 +113,11 @@ export async function buildApp({ configStore, clientRegistry, logger = false, st
   app.post('/api/instances/:id/login', async (request, reply) => {
     const client = findClient(request.params.id, reply); if (!client) return
     const supplied = Object.hasOwn(request.body || {}, 'password')
-    return { ...(await client.ensureAuthenticated(supplied ? { credential: request.body.password } : {})), hasSavedPassword: Boolean(configStore.snapshot.instances.find(item => item.id === request.params.id)?.auth?.password) }
+    try {
+      return { ...(await client.ensureAuthenticated(supplied ? { credential: request.body.password } : {})), hasSavedPassword: Boolean(configStore.snapshot.instances.find(item => item.id === request.params.id)?.auth?.password) }
+    } catch (error) {
+      return reply.code(502).send({ error: 'upstream request failed' })
+    }
   })
   app.post('/api/instances/:id/logout', async (request, reply) => {
     const client = findClient(request.params.id, reply); if (!client) return