deploy: upstream Ollama auth token + adoptable data volumes

Two production-hardening changes triggered by real issues found on the
first prod attempt against neuronetz-ai-01.

1. Upstream auth (the production Ollama is fronted by an auth proxy):

   - New config: OLLAMA_AUTH_TOKEN (pydantic SecretStr — never appears in
     repr/logs/errors), plus OLLAMA_AUTH_HEADER (default "Authorization")
     and OLLAMA_AUTH_SCHEME (default "Bearer") for stacks that expect a
     non-standard header like X-API-Key.
   - lifespan._build_upstream_headers() injects the configured header into
     the single shared httpx client used by both the proxy hot path AND
     the discovery poller, so /api/tags + /api/chat both authenticate
     against the upstream automatically.
   - New CLI: `neuronetz-gateway probe-ollama` — uses the same client
     config to GET /api/version and /api/tags, reports success/transport-
     error/HTTP-status, lists the first few discovered models, exits 1 on
     any failure. The token itself is never printed (only whether one
     was attached). Lets ops verify upstream reachability before letting
     real traffic through.
   - docker-compose.yml passes OLLAMA_AUTH_TOKEN/HEADER/SCHEME through;
     .env.example documents them with a leave-blank-for-internal-Ollama
     default.

2. Volume adoption (don't lose existing model data on re-deploy):

   - docker-compose.yml now pins absolute Docker volume NAMES for both
     postgres_data and ollama_data, configurable via POSTGRES_DATA_VOLUME
     and OLLAMA_DATA_VOLUME. Defaults preserve the previous per-project
     names so existing deployments aren't disturbed.
   - This addresses the scenario where deploying this compose under a new
     project directory created fresh, empty volumes alongside an existing
     `neuro-ollama_ollama-data` volume containing pre-pulled models (incl.
     deepseek-r1:14b, qwen2.5:14b, gemma3:12b, ...). Setting
     OLLAMA_DATA_VOLUME=neuro-ollama_ollama-data in .env tells the new
     stack to mount the existing volume in place — no copy, no downtime.
   - .env.example documents the override with the exact host's volume name
     as an example.

Both changes are ruff + mypy --strict clean.

src/neuronetz_gateway/config.py

@@ -8,7 +8,7 @@ from __future__ import annotations
 
 from functools import lru_cache
 
-from pydantic import Field
+from pydantic import Field, SecretStr
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
 
@@ -35,6 +35,16 @@ class Settings(BaseSettings):
     ollama_connect_timeout_s: int = Field(default=5)
     ollama_read_timeout_s: int = Field(default=600)
     ollama_max_connections: int = Field(default=64)
+    # Optional Bearer token sent to the upstream Ollama on EVERY request from the
+    # gateway (proxy hot path + the discovery poller). Use SecretStr so the value
+    # never appears in repr(), logs, or error messages. Empty/unset = no header.
+    ollama_auth_token: SecretStr | None = Field(default=None)
+    # If you front Ollama with an auth proxy that expects a non-standard header
+    # name (e.g. ``X-API-Key`` instead of ``Authorization``), override here.
+    # The scheme prefix (``Bearer ``) is dropped automatically when the header
+    # isn't ``Authorization``.
+    ollama_auth_header: str = Field(default="Authorization")
+    ollama_auth_scheme: str = Field(default="Bearer")
 
     # --- Model discovery (SPEC §4.6) ---
     model_discovery_refresh_s: int = Field(default=60)