fix(#37): make NIM a peer provider in config.example.toml + setup status

A user couldn't find an `NVIDIA_API_KEY` block in `~/.deepseek/config.toml`
because the example file only mentioned NIM as commented-out alternates
to the top-level keys. Two fixes:

- `config.example.toml` now has explicit `[providers.deepseek]` and
  `[providers.nvidia_nim]` sections (placed after all top-level keys so
  the TOML still parses cleanly), each documenting `api_key` /
  `base_url` / `model` plus the env vars that override them. Both
  providers can be stored at once and toggled via `/provider` or
  `--provider` without re-entering keys.
- `setup --status` "missing api_key" message is now provider-aware: on
  `nvidia-nim` it points at `NVIDIA_API_KEY` + `[providers.nvidia_nim]`
  + `deepseek auth set --provider nvidia-nim`, instead of the
  DeepSeek-only hint.

Audit verified: the v0.5.0 multi-turn replay fix path
(`should_replay_reasoning_content` → `requires_reasoning_content` in
`crates/tui/src/client.rs:1796`) keys off the model name (matches
`deepseek-v4`), not the provider, so NIM-hosted V4 models get the
replay automatically. No NIM-specific 400-class regression there.

Closes #37 (docs/UX); the live multi-turn-against-NIM verification
remains a manual smoke step listed in the issue (no NIM creds in CI).

config.example.toml

@@ -7,21 +7,19 @@
 # See `docs/CONFIGURATION.md` for how config is loaded (profiles, env overrides, etc.).
 
 # ─────────────────────────────────────────────────────────────────────────────────
-# API Keys
+# Active provider + DeepSeek defaults
 # ─────────────────────────────────────────────────────────────────────────────────
+# Choose which provider to use by default. Per-provider credentials live in the
+# `[providers.deepseek]` and `[providers.nvidia_nim]` sections near the bottom of
+# this file — keeping both stored at once means `/provider deepseek` and
+# `/provider nvidia-nim` (or `--provider nvidia-nim`) toggle without having to
+# re-enter keys. Top-level `api_key` / `base_url` are still read as DeepSeek
+# defaults when `[providers.deepseek]` is absent (backward compatibility).
 provider = "deepseek" # deepseek | nvidia-nim
 api_key = "YOUR_DEEPSEEK_API_KEY" # must be non-empty
-
-# ─────────────────────────────────────────────────────────────────────────────────
-# Base URLs
-# ─────────────────────────────────────────────────────────────────────────────────
 base_url = "https://api.deepseek.com"
 # base_url = "https://api.deepseeki.com"         # China users
 # base_url = "https://api.deepseek.com/beta"     # DeepSeek beta features such as strict tool mode
-# For NVIDIA NIM-hosted DeepSeek:
-# provider = "nvidia-nim"
-# api_key = "YOUR_NVIDIA_API_KEY"
-# base_url = "https://integrate.api.nvidia.com/v1"
 
 # ─────────────────────────────────────────────────────────────────────────────────
 # Default Models
@@ -70,6 +68,28 @@ max_subagents = 5 # optional (1-20)
 # managed_config_path = "/etc/deepseek/managed_config.toml"
 # requirements_path = "/etc/deepseek/requirements.toml"
 
+# ─────────────────────────────────────────────────────────────────────────────────
+# Per-provider credentials (peer providers — NIM is first-class, not a flag)
+# ─────────────────────────────────────────────────────────────────────────────────
+# Both providers can be stored at once; `provider = "..."` (top of file) or
+# `/provider deepseek` / `/provider nvidia-nim` switches between them without
+# having to re-enter keys. Env vars override anything set here:
+#   DeepSeek: DEEPSEEK_API_KEY, DEEPSEEK_BASE_URL, DEEPSEEK_MODEL
+#   NIM:      NVIDIA_API_KEY (or NVIDIA_NIM_API_KEY), NIM_BASE_URL
+#             (or NVIDIA_NIM_BASE_URL / NVIDIA_BASE_URL), NVIDIA_NIM_MODEL
+
+# DeepSeek Platform (https://platform.deepseek.com)
+[providers.deepseek]
+# api_key = "YOUR_DEEPSEEK_API_KEY"
+# base_url = "https://api.deepseek.com"
+# model = "deepseek-v4-pro"
+
+# NVIDIA NIM-hosted DeepSeek V4 (https://build.nvidia.com)
+[providers.nvidia_nim]
+# api_key = "YOUR_NVIDIA_API_KEY"
+# base_url = "https://integrate.api.nvidia.com/v1"
+# model = "deepseek-ai/deepseek-v4-pro"     # or deepseek-ai/deepseek-v4-flash
+
 # ─────────────────────────────────────────────────────────────────────────────────
 # TUI
 # ─────────────────────────────────────────────────────────────────────────────────

crates/tui/src/main.rs

@@ -1118,10 +1118,25 @@ fn run_setup_status(config: &Config, workspace: &Path) -> Result<()> {
             "  {} api_key: set via config",
             "✓".truecolor(aqua_r, aqua_g, aqua_b)
         ),
-        ApiKeySource::Missing => println!(
-            "  {} api_key: missing  (set DEEPSEEK_API_KEY or run `deepseek login`)",
-            "✗".truecolor(red_r, red_g, red_b)
-        ),
+        ApiKeySource::Missing => {
+            let (env_var, login_hint) = match config.api_provider() {
+                crate::config::ApiProvider::NvidiaNim => (
+                    "NVIDIA_API_KEY",
+                    "deepseek auth set --provider nvidia-nim --api-key \"...\"",
+                ),
+                crate::config::ApiProvider::Deepseek => {
+                    ("DEEPSEEK_API_KEY", "deepseek login --api-key \"...\"")
+                }
+            };
+            println!(
+                "  {} api_key: missing  (set {env_var} or `[providers.{}].api_key` in ~/.deepseek/config.toml; or run `{login_hint}`)",
+                "✗".truecolor(red_r, red_g, red_b),
+                match config.api_provider() {
+                    crate::config::ApiProvider::NvidiaNim => "nvidia_nim",
+                    crate::config::ApiProvider::Deepseek => "deepseek",
+                }
+            );
+        }
     }
     println!(
         "  · base_url: {}",