feat(llm-inference-multimodel): codify Phi-3.5-mini + Llama-3.1-8B GGUF staging (t_730f9584)

Adds idempotent, data-driven GGUF staging for the two new router models on
astro-orbiter alongside the production Qwen3.6-35B-A3B-UD-Q4_K_S. Both files
were already staged live (byte-exact); this commit codifies them in Ansible so
future re-runs and any new model adds are version-controlled and audit-friendly.

Changes:
- roles/llm-inference-multimodel/tasks/stage_model.yml (NEW)
  Idempotent per-model task: stat -> exact byte-size guard -> conditional
  get_url -> ownership/mode ensure -> notify router restart handler only on
  actual download. Loops from models.yml; nothing hardcoded.

- roles/llm-inference-multimodel/tasks/models.yml
  Appends the stage_model.yml loop (tagged: models) after the existing Qwen3.6
  download tasks. Data driven from host_vars/astro-orbiter/vars.yml.

- roles/llm-inference-multimodel/defaults/main.yml
  Adds llm_staged_models: [] default (empty = safe no-op for hosts with no
  staged model list defined).

- roles/llm-inference-multimodel/handlers/main.yml
  Adds 'restart llama-server-router on new GGUF' handler. Only fires when
  stage_model.yml performs an actual download or corrects ownership/mode.
  Normal idempotent re-runs (files already correct) do NOT fire this handler.

- host_vars/astro-orbiter/vars.yml
  Adds llm_staged_models list with the two new models:
    * Phi-3.5-mini-instruct-Q8_0.gguf (4,061,222,688 bytes,
      bartowski/Phi-3.5-mini-instruct-GGUF)
    * Meta-Llama-3.1-8B-Instruct-Q4_K_M.gguf (4,920,739,232 bytes,
      bartowski/Meta-Llama-3.1-8B-Instruct-GGUF)

- playbooks/day1_deploy_llm_inference_multimodel.yml
  Updates header comment: removes stale 'Semaphore broken' note, documents
  the correct execution channel (Semaphore template
  llm_inference_multimodel_stage_models, --tags models).

- group_vars/all/semaphore.yml
  Adds llm_inference_multimodel_stage_models template entry (config-as-code).
  Template is scoped to --tags models explicitly. Phase 4 (verify) is
  EXCLUDED: verify.yml starts llama-server-qwen on :8002, which would collide
  with the production llama-server-router.service already running on :8002.

Semaphore template created via API: project 1 / template id 19.
Execution: triggered immediately after this commit via Semaphore REST API.

ansible/roles/llm-inference-multimodel/handlers/main.yml

@@ -23,3 +23,15 @@
     daemon_reload: true
   become: true
   listen: "reload systemd"
+
+# Restart the llama.cpp router so it re-discovers /opt/models after a NEW GGUF
+# is staged. NOTIFIED ONLY from tasks/stage_model.yml when an actual download
+# (or permission correction) occurs — a normal idempotent re-run that finds the
+# files already correct will NOT fire this, so the live router is left
+# untouched. Safe on the idle GPU (router holds no resident model when all
+# entries are "unloaded"; restart is sub-second).
+- name: restart llama-server-router on new GGUF
+  ansible.builtin.systemd:
+    name: "{{ llm_router_service_name | default('llama-server-router') }}"
+    state: restarted
+  become: true