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/group_vars/all/semaphore.yml

@@ -152,3 +152,28 @@ semaphore_config:
           required: true
           type: TextVar
           default_value: "all"
+
+    - name: "llm_inference_multimodel_stage_models"
+      description: >-
+        Stage additional GGUF models into /opt/models on astro-orbiter via the
+        llm-inference-multimodel role (--tags models only). Idempotent: skips
+        files already present at the correct byte size. Notifies the
+        llama-server-router restart handler ONLY when a new GGUF is actually
+        downloaded. Does NOT touch Phase 4 (verify) or the legacy
+        llama-server-qwen service. Safe to run repeatedly.
+      app: ansible
+      playbook: ansible/playbooks/day1_deploy_llm_inference_multimodel.yml
+      inventory: production
+      repository: homelab
+      environment: default
+      vault_password: ansible-vault-pass
+      arguments: '["--tags","models","--diff"]'
+      # Scoped to --tags models:
+      #   Phase 0 (discover) -- skipped (no tag)
+      #   Phase 1 (models)   -- RUN (idempotent GGUF staging via stage_model.yml)
+      #   Phase 2 (systemd)  -- skipped
+      #   Phase 3 (firewall) -- skipped
+      #   Phase 4 (verify)   -- SKIPPED (collision risk: verify.yml would start
+      #                         llama-server-qwen on :8002, conflicting with the
+      #                         production llama-server-router.service. Excluded
+      #                         here deliberately. See t_730f9584.)