docs: drop early-beta framing for native Windows support (#36093)

Native Windows is out of beta. Removes the early-beta warnings, headings,
and rough-edge framing across the README and docs (EN + zh-Hans), keeping
the WSL2-only dashboard PTY caveat. Historical RELEASE_v0.14.0.md notes are
left intact since they accurately describe the state at that release.

- README: Windows install + cross-platform notes
- index.mdx, installation.md: headings, warning admonitions, parity note
- windows-native.md: title/sidebar_label/warning, provider-hunting tip
- contributing.md, nous-portal.md: cross-platform / Portal parity prose
- Repoint cross-links to the renamed installation#windows-native-powershell
  anchor (EN) and #windows原生powershell (zh, also fixes pre-existing drift)

website/docs/index.mdx

@@ -26,7 +26,7 @@ The self-improving AI agent built by [Nous Research](https://nousresearch.com).
 curl -fsSL https://raw.githubusercontent.com/NousResearch/hermes-agent/main/scripts/install.sh | bash
 ```
 
-**Windows (native, PowerShell)** — *early beta, [details →](/user-guide/windows-native)*
+**Windows (native, PowerShell)** — *[details →](/user-guide/windows-native)*
 
 ```powershell
 iex (irm https://raw.githubusercontent.com/NousResearch/hermes-agent/main/scripts/install.ps1)
@@ -48,7 +48,7 @@ It's not a coding copilot tethered to an IDE or a chatbot wrapper around a singl
 
 | | |
 |---|---|
-| 🚀 **[Installation](/getting-started/installation)** | Install in 60 seconds on Linux, macOS, WSL2, or native Windows (early beta) |
+| 🚀 **[Installation](/getting-started/installation)** | Install in 60 seconds on Linux, macOS, WSL2, or native Windows |
 | 📖 **[Quickstart Tutorial](/getting-started/quickstart)** | Your first conversation and key features to try |
 | 🗺️ **[Learning Path](/getting-started/learning-path)** | Find the right docs for your experience level |
 | ⚙️ **[Configuration](/user-guide/configuration)** | Config file, providers, models, and options |