Author LiteLLM AI proxy service (resolves #14)

Adds litellm + litellm-db to docker-compose.yml, litellm-config.yaml with
custom shadow-cost pricing (Claude Sonnet 5 reference, per #11) and a
priority-scheduling stub (per #16, needs real-hardware smoke test), and
required LITELLM_MASTER_KEY/SALT_KEY/DB_PASSWORD env vars. Untested on real
hardware — that's #17. Open WebUI/coding CLIs still talk to llama.cpp
directly, migration is #15.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

litellm-config.yaml

@@ -0,0 +1,24 @@
+model_list:
+  - model_name: qwen3.8-27b-local
+    litellm_params:
+      model: openai/${LLAMA_MODEL_FILE:-Qwen3.8-27B-UD-Q4_K_XL.gguf}
+      api_base: http://llama-server:8080/v1
+      api_key: local
+    model_info:
+      # Shadow cloud-cost estimate — priced against Claude Sonnet 5's published
+      # rate, not real spend (this proxy only ever routes to the local model).
+      # Source: https://platform.claude.com/docs/en/about-claude/pricing,
+      # checked 2026-08-25. Update these two numbers if that page changes.
+      input_cost_per_token: 0.000002   # $2 / MTok
+      output_cost_per_token: 0.00001   # $10 / MTok
+
+router_settings:
+  # ponytail: LiteLLM's request-prioritization scheduler is beta (see
+  # docs/proxy-request-priority.md) — exact settings key/shape must be
+  # confirmed against LiteLLM's current docs and smoke-tested against
+  # llama.cpp before workloads depend on it. Single-instance deployment,
+  # no Redis configured — add one only if the scheduler turns out to need it.
+  enable_priority_scheduling: true
+
+general_settings:
+  master_key: os.environ/LITELLM_MASTER_KEY