Add Ollama Cloud support with Base URL and API Key configuration (#692)

* Add Ollama Cloud support with Base URL and API Key configuration

* implemented feedback

* fix: use OLLAMA_BASE_URL env fallback in validate-model endpoint

* Remove dedicated Ollama configuration block

* security(ollama): prevent API key leak to client-controlled URLs

* added test

* fix: security hardening and Ollama Cloud default URL

- Add server OLLAMA_API_KEY fallback to validate-model endpoint with
  SSRF guard mirroring ai-providers.ts
- Tighten top-level SSRF exemption: only exempt Ollama when no server
  OLLAMA_API_KEY is configured
- Update Electron config to support OLLAMA_API_KEY env var
- Change default Ollama URL from localhost:11434 to ollama.com/api
  (Ollama Cloud) for web UI users
- Add tests for server env combo, API-key-only, and SSRF guard scenarios

---------

Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

env.example

@@ -59,8 +59,9 @@ AI_MODEL=global.anthropic.claude-sonnet-4-5-20250929-v1:0
 # AZURE_REASONING_EFFORT=low                 # Optional: Azure reasoning effort (low, medium, high)
 # AZURE_REASONING_SUMMARY=detailed
 
-# Ollama (Local) Configuration
-# OLLAMA_BASE_URL=http://localhost:11434/api  # Optional, defaults to localhost
+# Ollama Configuration (Local or Cloud)
+# OLLAMA_BASE_URL=https://ollama.com/api  # Optional, defaults to Ollama Cloud
+# OLLAMA_API_KEY=your-ollama-cloud-api-key    # Optional: For Ollama Cloud or authenticated remote instances
 # OLLAMA_ENABLE_THINKING=true                 # Optional: Enable thinking for models that support it (e.g., qwen3)
 
 # OpenRouter Configuration