feat: implement Extensions with real FreeSWITCH directory integration

- extensions table (tenant-scoped, RLS): number, sip_password_enc
  (AES-256-GCM via packages/shared/src/crypto.ts), caller_id, context,
  sofia_profile, codecs, max_registrations
- apps/api/src/extensions: CRUD (POST/GET/GET:id/DELETE), protected by a
  new generic PermissionGuard (@RequirePermission decorator), tenant
  resolved only from the JWT (never trusted from the client)
- SIP password is returned in plaintext only once, in the create response;
  toPublicExtension() explicitly destructures the encrypted field out
  (not a spread) so it can't leak by accident
- b2bcall-fs-config now resolves real directory data: Tenant.telephonyDomain
  -> Extension.number, decrypts the password, builds proper directory XML
  including a dial-string param (missing it caused originate to fail with
  MANDATORY_IE_MISSING instead of the expected USER_NOT_REGISTERED)
- pinned FreeSWITCH's 357737{domain} to a stable value (b2bcall.local) via a
  vars.xml patch in the Dockerfile -- it previously used the container's
  dynamic IP, which could never match a stored telephony_domain
- added HTTP Basic auth between FreeSWITCH and fs-config
  (gateway-credentials, timingSafeEqual comparison) now that the service
  returns real secret data, closing the gap flagged as pending in the XML
  Curl phase instead of leaving it open
- found and fixed: PermissionGuard's constructor-injected Reflector came
  back undefined at runtime under tsx/esbuild (unreliable cross-file
  decorator metadata emission) -- fixed with an explicit @Inject(Reflector);
  worth watching for in future guards/services run via tsx
- verified end-to-end: create extension -> originate user/<ext> reports
  USER_NOT_REGISTERED (found, not registered) -> delete -> back to
  SUBSCRIBER_ABSENT (not found); password never reappears in any GET;
  unauthenticated fs-config requests get 401
- docs/EXTENSIONS.md

packages/telephony/src/directory-xml.ts

@@ -0,0 +1,72 @@
+/** Escapa texto pra uso seguro dentro de atributos/elementos XML. */
+function xmlEscape(value: string): string {
+  return value
+    .replace(/&/g, "&")
+    .replace(/</g, "&lt;")
+    .replace(/>/g, "&gt;")
+    .replace(/"/g, "&quot;")
+    .replace(/'/g, "&apos;");
+}
+
+export interface DirectoryUserParams {
+  domain: string;
+  extensionNumber: string;
+  extensionName: string;
+  sipPassword: string;
+  context: string;
+  callerIdName?: string;
+  callerIdNumber?: string;
+  tenantId: string;
+  extensionId: string;
+}
+
+/**
+ * Monta o XML de directory que o FreeSWITCH espera do mod_xml_curl pra
+ * autenticar/rotear um ramal (agente.md secao 26). `b2bcall_tenant_id` e
+ * `b2bcall_extension_id` viram channel variables em toda chamada desse
+ * ramal — é assim que o resto do sistema volta a saber de qual tenant uma
+ * chamada é (secao 81).
+ */
+export function buildDirectoryUserXml(params: DirectoryUserParams): string {
+  const callerIdName = xmlEscape(params.callerIdName ?? params.extensionName);
+  const callerIdNumber = xmlEscape(params.callerIdNumber ?? params.extensionNumber);
+
+  return `<?xml version="1.0" encoding="UTF-8"?>
+<document type="freeswitch/xml">
+  <section name="directory">
+    <domain name="${xmlEscape(params.domain)}">
+      <params>
+        <!-- Sem isto, o endpoint "user/" nao sabe montar o dialstring pra
+             alcançar o contato registrado (mesmo padrão da config vanilla
+             em directory/default.xml). -->
+        <param name="dial-string" value="{^^:sip_invite_domain=\${dialed_domain}:presence_id=\${dialed_user}@\${dialed_domain}}\${sofia_contact(*/\${dialed_user}@\${dialed_domain})}"/>
+      </params>
+      <groups>
+        <group name="default">
+          <users>
+            <user id="${xmlEscape(params.extensionNumber)}">
+              <params>
+                <param name="password" value="${xmlEscape(params.sipPassword)}"/>
+              </params>
+              <variables>
+                <variable name="user_context" value="${xmlEscape(params.context)}"/>
+                <variable name="effective_caller_id_name" value="${callerIdName}"/>
+                <variable name="effective_caller_id_number" value="${callerIdNumber}"/>
+                <variable name="b2bcall_tenant_id" value="${xmlEscape(params.tenantId)}"/>
+                <variable name="b2bcall_extension_id" value="${xmlEscape(params.extensionId)}"/>
+              </variables>
+            </user>
+          </users>
+        </group>
+      </groups>
+    </domain>
+  </section>
+</document>`;
+}
+
+export const NOT_FOUND_XML = `<?xml version="1.0" encoding="UTF-8"?>
+<document type="freeswitch/xml">
+  <section name="result">
+    <result status="not found"/>
+  </section>
+</document>`;