Add NIM env support and .env.example template

.env.example

@@ -0,0 +1,44 @@
+# DeepSeek TUI environment
+# Shell-exported variables override values in this file.
+# Copy this file to `.env`, then uncomment only the values you want to use.
+
+# DeepSeek API (default provider)
+# Get an API key from DeepSeek, then keep it local in `.env`.
+DEEPSEEK_API_KEY=
+
+# Global endpoint:
+# DEEPSEEK_BASE_URL=https://api.deepseek.com
+# China endpoint:
+# DEEPSEEK_BASE_URL=https://api.deepseeki.com
+
+# V4 model selection. Compatibility aliases such as `deepseek-chat` normalize
+# to the current V4 flash model in the TUI.
+# DEEPSEEK_MODEL=deepseek-v4-pro
+# DEEPSEEK_MODEL=deepseek-v4-flash
+
+# NVIDIA NIM-hosted DeepSeek V4
+# Use this provider when routing through NVIDIA's OpenAI-compatible endpoint.
+# DEEPSEEK_PROVIDER=nvidia-nim
+# NVIDIA_API_KEY=
+# NVIDIA_NIM_API_KEY=
+# NVIDIA_NIM_BASE_URL=https://integrate.api.nvidia.com/v1
+# NIM_BASE_URL=https://integrate.api.nvidia.com/v1
+# NVIDIA_BASE_URL=https://integrate.api.nvidia.com/v1
+# NVIDIA_NIM_MODEL=deepseek-ai/deepseek-v4-pro
+
+# Logging
+# `DEEPSEEK_LOG_LEVEL` is forwarded by the facade; `RUST_LOG` enables the
+# TUI's lightweight verbose logs for info/debug/trace directives.
+# DEEPSEEK_LOG_LEVEL=debug
+# RUST_LOG=deepseek_tui=debug
+
+# Agent safety defaults
+# `on-request` asks before higher-risk work; `workspace-write` keeps writes
+# inside the workspace unless a sandbox elevation path is explicitly used.
+# DEEPSEEK_APPROVAL_POLICY=on-request
+# DEEPSEEK_SANDBOX_MODE=workspace-write
+# DEEPSEEK_ALLOW_SHELL=true
+
+# Optional extension paths
+# DEEPSEEK_SKILLS_DIR=~/.deepseek/skills
+# DEEPSEEK_MCP_CONFIG=~/.deepseek/mcp.json