Add .env.example with all configurable environment variables"

.env.example

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+# ═══════════════════════════════════════════════════════════════
+# Alpha Factory — Environment Configuration
+# ═══════════════════════════════════════════════════════════════
+# Copy this file to .env and fill in your values:
+#   cp .env.example .env
+#
+# The pipeline reads these automatically via os.getenv()
+# ═══════════════════════════════════════════════════════════════
+
+# ─── HuggingFace (cloud models) ───────────────────────────────
+# Get your token at: https://huggingface.co/settings/tokens
+# Required for cloud models (Qwen-72B, DeepSeek-V3, Llama-4, etc.)
+# Not needed if using only local Ollama models
+HF_TOKEN=hf_xxxxxxxxxxxxxxxxxxxxxxxxxxxx
+
+# ─── Ollama (local models) ────────────────────────────────────
+# Default: http://localhost:11434
+# Change if running Ollama on a different machine/port
+OLLAMA_URL=http://localhost:11434
+
+# ─── WorldQuant BRAIN API ─────────────────────────────────────
+# Your BRAIN session credentials
+# Get these from browser devtools after logging into brain.worldquant.com
+# Network tab → any API request → copy cookie/authorization header
+BRAIN_API_URL=https://api.worldquantbrain.com
+BRAIN_SESSION_TOKEN=your_session_token_here
+
+# ─── Pipeline Settings ────────────────────────────────────────
+# Root directory for all pipeline data (factor store, logs, prompts)
+AF_ROOT=.
+
+# Batch size: how many alpha candidates to generate per run
+AF_BATCH_SIZE=10
+
+# Max BRAIN submissions per day (kill switch)
+AF_DAILY_SUBMISSIONS_MAX=200
+
+# ─── Model Defaults (used when not in interactive mode) ───────
+# These are Ollama model names for local inference
+# Override by running with --interactive flag
+AF_MICROFISH_MODEL=qwen2.5:1.5b
+AF_TINYFISH_MODEL=qwen2.5:3b
+AF_MEDIUMFISH_MODEL=qwen2.5:7b
+AF_BIGFISH_MODEL=qwen2.5:14b
+
+# ─── LLM Server (if using vLLM instead of Ollama) ────────────
+# Uncomment if you're running vLLM or another OpenAI-compatible server
+# LLM_BASE_URL=http://localhost:8000/v1
+# LLM_API_KEY=dummy
+
+# ─── RAG / Paper Index ────────────────────────────────────────
+# ChromaDB persistence directory for arXiv paper embeddings
+CHROMA_PERSIST_DIR=./data/chroma
+
+# ─── Logging ──────────────────────────────────────────────────
+# Langfuse (optional — self-hosted trace logging)
+# LANGFUSE_HOST=http://localhost:3000
+# LANGFUSE_PUBLIC_KEY=pk-xxx
+# LANGFUSE_SECRET_KEY=sk-xxx
+
+# ─── Advanced ─────────────────────────────────────────────────
+# Fitness function thresholds (tune after 20+ alphas)
+AF_MIN_SHARPE_LOCAL=1.0
+AF_CORRELATION_THRESHOLD=0.65
+AF_MAX_ITERATIONS_PER_FAMILY=3