Add AI_PROVIDER and AI_MODEL support

docs/configuration.md

@@ -4,15 +4,29 @@ All configuration is managed in `tools/ai-review/config.yml`.
 
 ## Provider Settings
 
+The provider and model can be configured via Gitea secrets, so you don't need to edit `config.yml` per deployment:
+
+| Secret | Description | Example values |
+|--------|-------------|----------------|
+| `AI_PROVIDER` | Which LLM provider to use | `openai`, `openrouter`, `ollama`, `anthropic`, `azure`, `gemini` |
+| `AI_MODEL` | Model for the active provider | `gpt-4.1-mini`, `claude-3-5-sonnet-20241022`, `google/gemini-2.0-flash` |
+
+These secrets override the values in `config.yml`, which serve as fallback defaults.
+
 ```yaml
-# LLM Provider: openai | openrouter | ollama
+# LLM Provider: openai | openrouter | ollama | anthropic | azure | gemini
+# Override with the AI_PROVIDER Gitea secret.
 provider: openai
 
 # Model per provider
+# Override the active provider's model with the AI_MODEL Gitea secret.
 model:
   openai: gpt-4.1-mini
   openrouter: anthropic/claude-3.5-sonnet
   ollama: codellama:13b
+  anthropic: claude-3-5-sonnet-20241022
+  azure: gpt-4
+  gemini: gemini-1.5-pro
 
 # Generation settings
 temperature: 0        # 0 = deterministic
@@ -166,6 +180,8 @@ These override config file settings:
 
 | Variable | Description |
 |----------|-------------|
+| `AI_PROVIDER` | Override the active provider (e.g. `openrouter`, `anthropic`) |
+| `AI_MODEL` | Override the model for the active provider |
 | `AI_REVIEW_TOKEN` | Gitea/GitHub API token |
 | `AI_REVIEW_API_URL` | API base URL (`https://api.github.com` or Gitea URL) |
 | `AI_REVIEW_REPO` | Target repository (owner/repo) |