feat(llm-router): switch to --models-preset mode; add Phi-3.5-mini-instruct-8bit alias (t_9adf0889)

- Add templates/llama-server-router-preset.ini.j2: defines all 3 router GGUFs
  (Qwen3.6-35B, Phi-3.5-mini-Q8_0, Meta-Llama-3.1-8B) with explicit ctx-size,
  gpu-layers, cache settings carried over from --models-dir baseline. The Phi
  entry adds alias=Phi-3.5-mini-instruct-8bit (Ryan's aux.title_generation target).

- Update templates/llama-server-router.service.j2: Jinja2 conditional emits
  --models-preset <path> when llm_router_preset_enabled=true, otherwise
  --models-dir (backward compat, default unchanged).

- Add tasks/preset.yml: deploy preset INI, restart router on change, verify
  both Phi-3.5-mini-instruct-Q8_0 (primary) and Phi-3.5-mini-instruct-8bit
  (alias) appear in /v1/models, plus Qwen and Llama IDs unchanged.

- Update defaults/main.yml: add llm_router_preset_enabled (default false) and
  llm_router_preset_path=/opt/llama-server-router-preset.ini.

- Update tasks/main.yml: import preset.yml as Phase P (gated, no-op by default).
- Update handlers/main.yml: add 'restart router' handler for preset changes.
- Add playbooks/day2_add_phi_alias.yml: single-command deployment.

GH #22364 note: --models-preset mode creates an extra 'default' entry in
/v1/models — cosmetic, does not affect model selection by name.

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

@@ -10,7 +10,11 @@ User={{ llm_service_user }}
 Group={{ llm_service_user }}
 Environment="HOME=/home/{{ llm_service_user }}"
 ExecStart={{ llm_binary_path }} \
+{% if llm_router_preset_enabled | default(false) %}
+    --models-preset {{ llm_router_preset_path }} \
+{% else %}
     --models-dir {{ llm_router_models_dir }} \
+{% endif %}
     --models-max {{ llm_router_models_max }} \
     --host {{ llm_router_bind_address }} \
     --port {{ llm_router_port }} \
@@ -24,19 +28,23 @@ ExecStart={{ llm_binary_path }} \
     --parallel {{ llm_router_parallel }} \
     --metrics
 
-# ROUTER MODE NOTES (2026-08-12, t_0cca74a2):
+# ROUTER MODE NOTES (2026-08-12, t_0cca74a2 / updated t_9adf0889):
 # - 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).
+#   Without -m, llama-server discovers all .gguf files in --models-dir, or uses
+#   the per-model definitions in a --models-preset INI file.
+# - PRESET MODE (t_9adf0889, 2026-08-12):
+#   llm_router_preset_enabled=true switches from --models-dir to --models-preset.
+#   Preset mode adds alias support (--models-dir cannot assign aliases).
+#   The preset INI is at {{ llm_router_preset_path | default('/opt/llama-server-router-preset.ini') }}.
+#   Both the section name and the alias field in the INI work as model IDs.
+#   GH #22364 (extra "default" entry in /v1/models) is expected in preset mode — cosmetic.
 # - --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
+# - Clients select a model via "model": "<section-name-or-alias>" in their
 #   chat completion request. Hermes sends model: "<id>" on every request already.
 # - Cold model load on first request: ~30-60s for Qwen3.6-35B. First response
 #   will be slow. This is expected. Document in runbook.