feat: add image generation for OpenAI DALL-E and Gemini Imagen

New `/v1/images/generations` endpoint proxies DALL-E 2/3 (OpenAI)
and Imagen 3 (Gemini). Same auth/logging as chat completions.

- Add ImageGenerationRequest/Response models
- Extend Provider interface with ImageGeneration()
- OpenAI: forward to /v1/images/generations
- Gemini: call /v1beta/models/{model}:predict, map OpenAI params
- Circuit breaker wraps image gen like chat completions
- Model routing: dall-e* -> openai, imagen*/gemini* -> gemini
- Unsupported providers (deepseek/moonshot/grok/ollama) return error
- Fix pre-existing CachedContentTokenCount bug in StreamGemini

README.md

@@ -4,10 +4,10 @@ A unified, high-performance LLM proxy gateway built in Go. It provides a single
 
 ## Features
 
-- **Unified API:** OpenAI-compatible `/v1/chat/completions` and `/v1/models` endpoints.
+- **Unified API:** OpenAI-compatible `/v1/chat/completions`, `/v1/images/generations`, and `/v1/models` endpoints.
 - **Multi-Provider Support:**
-  - **OpenAI:** GPT-4o, GPT-4o Mini, o1, o3 reasoning models.
-  - **Google Gemini:** Gemini 2.0 Flash, Pro, and vision models (with native CoT support).
+  - **OpenAI:** GPT-4o, GPT-4o Mini, o1, o3 reasoning models, DALL-E 2/3 image generation.
+  - **Google Gemini:** Gemini 2.0 Flash, Pro, and vision models (with native CoT support), Imagen 3 image generation.
   - **DeepSeek:** DeepSeek Chat and Reasoner (R1) models.
   - **Moonshot:** Kimi K2.5 and other Kimi models.
   - **xAI Grok:** Grok-4 models.
@@ -18,6 +18,7 @@ A unified, high-performance LLM proxy gateway built in Go. It provides a single
   - **Database Persistence:** Every request logged to SQLite for historical analysis and dashboard analytics.
   - **Streaming Support:** Full SSE (Server-Sent Events) support for all providers.
 - **Multimodal (Vision):** Image processing (Base64 and remote URLs) across compatible providers.
+- **Image Generation:** DALL-E 2/3 (OpenAI) and Imagen 3 (Gemini) via OpenAI-compatible `/v1/images/generations` endpoint.
 - **Multi-User Access Control:**
   - **Admin Role:** Full access to all dashboard features, user management, and system configuration.
   - **Viewer Role:** Read-only access to usage analytics, costs, and monitoring.
@@ -54,6 +55,7 @@ GopherGate is designed with security in mind:
 ### Quick Start
 
 1. Clone and build:
+
    ```bash
    git clone <repository-url>
    cd gophergate
@@ -61,6 +63,7 @@ GopherGate is designed with security in mind:
    ```
 
 2. Configure environment:
+
    ```bash
    cp .env.example .env
    # Edit .env and add your configuration:
@@ -112,6 +115,7 @@ Access the dashboard at `http://localhost:8080`.
 
 **Forgot Password?**
 You can reset the admin password to default by running:
+
 ```bash
 ./gophergate -reset-admin
 ```
@@ -129,6 +133,7 @@ endpoint after enabling Ollama in configuration and setting the base URL to your
 Ollama server (default: `http://localhost:11434/v1`).
 
 ### Python
+
 ```python
 from openai import OpenAI
 
@@ -141,6 +146,35 @@ response = client.chat.completions.create(
     model="gpt-4o",
     messages=[{"role": "user", "content": "Hello!"}]
 )
+
+### Image Generation (DALL-E / Imagen)
+
+```python
+from openai import OpenAI
+
+client = OpenAI(
+    base_url="http://localhost:8080/v1",
+    api_key="YOUR_CLIENT_API_KEY"
+)
+
+# DALL-E 3 (OpenAI)
+resp = client.images.generate(
+    model="dall-e-3",
+    prompt="A cute gopher wearing a top hat",
+    n=1,
+    size="1024x1024"
+)
+print(resp.data[0].url)
+
+# Imagen 3 (Gemini) — uses same endpoint
+resp = client.images.generate(
+    model="imagen-3.0-generate-001",
+    prompt="A gopher coding in Go",
+    n=1,
+    size="1024x1024"
+)
+print(resp.data[0].url)  # Returns data URI (Gemini returns base64)
+```
 ```
 
 ## License