feat: activate mod_xml_curl with b2bcall-fs-config (agente.md secao 26)

- apps/freeswitch-config (b2bcall-fs-config): Fastify service implementing
  the mod_xml_curl HTTP protocol (form-encoded POST -> XML response),
  containerized, no host port published
- reactivated mod_xml_curl in FreeSWITCH, binding restricted to
  directory|dialplan only (configuration was removed after testing showed
  it firing several unnecessary HTTP round-trips at boot for module
  configs we don't need dynamic — matches agente.md's own 'don't put every
  critical config through XML Curl' guidance)
- no extensions/dialplan tables exist yet (next phases), so the service
  always answers 'not found' for now — this phase only proves the wire
  protocol works without breaking the static vanilla config fallback
- verified end-to-end: user/8888 (nowhere) -> SUBSCRIBER_ABSENT via
  fs-config; user/1000 (static vanilla extension) -> USER_NOT_REGISTERED,
  proving FreeSWITCH correctly falls through to static XML when xml_curl
  says not found
- docs/XML_CURL.md, including the not-yet-authenticated endpoint note (fine
  while it only returns not-found; needs gateway-credentials before serving
  real directory/dialplan data)

apps/freeswitch-config/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "@b2bcall/freeswitch-config",
+  "version": "0.0.1",
+  "private": true,
+  "scripts": {
+    "dev": "tsx watch src/main.ts",
+    "build": "tsc -p tsconfig.json",
+    "start": "node dist/main.js",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@b2bcall/shared": "workspace:*",
+    "@fastify/formbody": "^8.0.1",
+    "fastify": "5.12.1"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "tsx": "^4.23.12",
+    "typescript": "^5.7.0"
+  }
+}