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/developer-guide/contributing.md

@@ -94,7 +94,7 @@ pytest tests/ -v
 
 ## Cross-Platform Compatibility
 
-Hermes officially supports **Linux, macOS, WSL2, and native Windows (early beta — via PowerShell install)**.  Native Windows uses Git Bash (from [Git for Windows](https://git-scm.com/download/win)) for shell commands.  A few features require POSIX kernel primitives and are gated: the dashboard's embedded PTY terminal pane (`/chat` tab) is WSL2-only. The native-Windows path is new and moves fast — if you're doing Windows-heavy dev, expect to hit and fix rough edges.
+Hermes officially supports **Linux, macOS, WSL2, and native Windows (via PowerShell install)**.  Native Windows uses Git Bash (from [Git for Windows](https://git-scm.com/download/win)) for shell commands.  A few features require POSIX kernel primitives and are gated: the dashboard's embedded PTY terminal pane (`/chat` tab) is WSL2-only. If you're doing Windows-heavy dev, run the Windows-footgun lint (`scripts/check-windows-footguns.py`) before pushing.
 
 When contributing code, keep these rules in mind: