Add OLLAMA_NUM_CTX config to reduce VRAM usage

Replaces the hardcoded num_ctx=32768 KV cache allocation with a
configurable env var defaulting to 8192. This significantly reduces
VRAM pressure when multiple services share the GPU.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/config.py

@@ -27,6 +27,9 @@ class Config:
     # Optional dedicated model for intent classification (should be small/fast).
     # Falls back to OLLAMA_MODEL if not set. Can also be overridden per-user via settings.
     OLLAMA_INTENT_MODEL: str = os.environ.get("OLLAMA_INTENT_MODEL", "")
+    # KV cache context window for generation. Lower = less VRAM, less throughput impact.
+    # 8192 is sufficient for most conversations; raise if you paste large documents.
+    OLLAMA_NUM_CTX: int = int(os.environ.get("OLLAMA_NUM_CTX", "8192"))
     SECRET_KEY: str = _read_secret("SECRET_KEY", "SECRET_KEY_FILE", "dev-secret-change-me")
     SECURE_COOKIES: bool = os.environ.get("SECURE_COOKIES", "").lower() in ("1", "true", "yes")
     LOG_LEVEL: str = os.environ.get("LOG_LEVEL", "INFO")