feat(llm-inference-multimodel): bump router --models-max 1->4 on astro-orbiter (t_33acbb2e)

Changes:
- host_vars/astro-orbiter/vars.yml: add llm_router_models_max: 4 (overrides
  conservative default of 1). Detailed VRAM OOM risk note included inline:
  worst-case 3-model co-residency ~31GB > 24GB RTX 3090. LRU eviction
  mitigates in single-user operation; flagged for Ryan's review.
- playbooks/day2_bump_router_models_max.yml: new targeted playbook; deploys
  updated router unit, restarts the live service, verifies /health 200 and
  /v1/models lists all 3 GGUFs post-restart.
- group_vars/all/semaphore.yml: add llm_router_update_unit template pointing
  at the new playbook.
- roles/llm-inference-multimodel/defaults/main.yml: update comment to reflect
  the var is now overridden in host_vars rather than 'hardcoded to 1'.
- roles/llm-inference-multimodel/templates/llama-server-router.service.j2:
  correct stale 'HARDCODED TO 1' comment — value is variable-driven.

Constraints honored:
- --parallel 1 left untouched (not in scope, not modified anywhere)
- No ad-hoc SSH/systemctl/curl state mutation; all execution via Semaphore
- No installed/vendored code patched

ansible/roles/llm-inference-multimodel/templates/llama-server-router.service.j2

@@ -28,9 +28,12 @@ ExecStart={{ llm_binary_path }} \
 # - NO -m/--model flag: this is what enables llama-server router/supervisor mode.
 #   Without -m, llama-server discovers all .gguf files in --models-dir, spawning
 #   each as its own child process on demand (LRU-eviction when over models-max).
-# - --models-max {{ llm_router_models_max }} is HARDCODED TO 1.
-#   Default cap is 4 simultaneous — OOM on 24GB with a 20GB model.
-#   Do not increase without a VRAM budget review (see defaults/main.yml comment).
+# - --models-max {{ llm_router_models_max }} is driven by llm_router_models_max
+#   (default 1 in defaults/main.yml; overridden to 4 in host_vars/astro-orbiter
+#   as of t_33acbb2e after VRAM budget review — see host_vars for OOM risk note).
+#   Default llama-server cap is 4 simultaneous — OOM on 24GB if all 3 current
+#   GGUFs load at once. LRU eviction mitigates in practice but review before adding
+#   models. See host_vars/astro-orbiter/vars.yml for full VRAM breakdown.
 # - --models-dir /opt/models: auto-discovers all .gguf files. Keep that directory
 #   clean (Qwen-only) to avoid spurious extra entries in /v1/models.
 # - Clients select a model via "model": "<gguf-basename-without-.gguf>" in their