Add LLM compose stack for phy-srv-gpu01 (not deployed yet)

Follows the homelab pattern: ironicbadger.docker_compose_generator v2
renders services/<host>/NN-<stack>/compose.yml templates into
~/docker/compose.yaml on the host.

- 01-vllm: chat model, fixed --gpu-memory-utilization
- 02-embeddings: second vLLM instance (--task embed) rather than a
  separate toolchain, so SM120 support only has to be solved once
- 03-openwebui: Open WebUI + pgvector (not chroma — corpus size)
- 99-network: shared bridge; leading comment keeps networks: top-level
- pin docker_compose_generator to 2.0.1 — galaxy tags mix v1/v2 formats
- group_vars: stack config incl. LDAP placeholders still to be filled

The role only writes the compose file; starting the stack stays manual.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ansible/requirements.yml

@@ -1,4 +1,7 @@
 ---
+# docker_compose_generator MUST stay pinned — its galaxy tags mix formats
+# (1.0.x uses a `containers:` data structure, 2.x uses native compose files)
+# and an unpinned install can silently change the expected layout.
 roles:
   #- name: geerlingguy.pip
   - name: geerlingguy.docker
@@ -6,3 +9,4 @@ roles:
   - name: geerlingguy.security
   - name: geerlingguy.ntp
   - name: ironicbadger.docker_compose_generator
+    version: 2.0.1