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/Dockerfile

@@ -0,0 +1,17 @@
+# syntax=docker/dockerfile:1.7
+FROM node:22-slim
+
+RUN corepack enable && corepack prepare pnpm@11.24.0 --activate
+
+WORKDIR /repo
+
+COPY pnpm-workspace.yaml package.json pnpm-lock.yaml tsconfig.base.json ./
+COPY packages/types packages/types
+COPY packages/shared packages/shared
+COPY apps/freeswitch-config apps/freeswitch-config
+
+RUN pnpm install --frozen-lockfile --filter @b2bcall/freeswitch-config...
+
+WORKDIR /repo/apps/freeswitch-config
+
+CMD ["pnpm", "exec", "tsx", "src/main.ts"]