Docs: Added v0.20.5 release notes. (#10014)

### What problem does this PR solve?

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### Type of change

- [x] Documentation Update

docs/release_notes.md

@@ -22,6 +22,31 @@ The embedding models included in a full edition are:
 These two embedding models are optimized specifically for English and Chinese, so performance may be compromised if you use them to embed documents in other languages.
 :::
 
+## v0.20.5
+
+Released on September 10, 2025.
+
+### Improvements
+
+- Agent Performance Optimized: Improved planning and reflection speed for simple tasks; optimized concurrent tool calls for parallelizable scenarios, significantly reducing overall response time.
+- Agent Prompt Framework exposed: Developers can now customize and override framework-level prompts in the system prompt section, enhancing flexibility and control.
+- Execute SQL Component Enhanced: Replaced the original variable reference component with a text input field, allowing free-form SQL writing with variable support.
+- Chat: Re-enabled Reasoning and Cross-language search.
+- Retrieval API Enhanced: Added metadata filtering support to the [Retrieve chunks](https://ragflow.io/docs/dev/http_api_reference#retrieve-chunks) method.
+
+### Added models
+
+- Meituan LongCat
+- Kimi: kimi-k2-turbo-preview and kimi-k2-0905-preview
+- Qwen: qwen3-max-preview
+- SiliconFlow: DeepSeek V3.1
+
+### Fixed issues
+
+- Dataset: Deleted files remained searchable.
+- Chat: Unable to chat with an Ollama model. 
+- Agent: Resolved issues including cite toggle failure, task mode requiring dialogue triggers, repeated answers in multi-turn dialogues, and duplicate summarization of parallel execution results.
+
 ## v0.20.4
 
 Released on August 27, 2025.