Update Linux docs for the first Linux release

[ivan-ottinger]

Related issues

• Resolves RSM-1304.

How AI was used in this PR

Claude Code drafted the rewrites. Reviewed by human.

Proposed Changes

Refresh the Linux docs to reflect that Linux is now a fully supported platform, and rework docs/linux.md to be a tighter contributor-focused doc.

README.md — adds Linux to the supported platforms list:

• "Mac and Windows" → "Mac, Windows, and Linux".
• Adds arch hints to all three bullets for consistency: macOS keeps (Intel or Apple Silicon); Windows and Linux get (x64 or ARM64).

docs/code-contributions.md — cleans up the platform-asymmetric Linux subsection:

• Drops "experimentally for Linux" from the Building Installers blurb.
• Notes Windows is also available in x64/ARM64 (was previously listed without arch detail).
• Replaces the stale Linux subsection (~17 lines describing a source-build flow with a now-false "auto-update not supported" caveat and a Wayland note) with a one-line pointer to ./linux.md.

docs/linux.md — refreshed in place:

• Drops the "experimental phase" framing.
• Drops both Wayland sections entirely: --enable-features=UseOzonePlatform is a no-op on Electron 28+, and --ozone-platform=wayland is an opt-in optimization, not a fix.
• Drops the "some features may behave differently".
• Drops the obvious launch step and the .desktop-registration footnote, since DEB installs handle both automatically.
• Splits the wp-studio:// URL handler registration out of the Desktop Shortcut section into its own H2. Different purpose (OAuth callback handling vs. app-launcher icon), and a contributor searching for "OAuth callback isn't reaching my dev build" wouldn't think to look under a shortcut heading. The xdg-mime step was originally added in Auth: Register wp-studio:// scheme on Linux #3205 with a real-bug rationale; this surfaces it.
• Reframes the file as contributor-focused: source-build steps, desktop shortcut, URL handler, and troubleshooting (permissions, AppArmor / Ubuntu 24.04+, missing system libs). The AppArmor note is now explicitly scoped to npm start-only.

Testing Instructions

• Read through the rewritten docs/linux.md end-to-end; verify the source-build flow, OAuth-handler registration, and troubleshooting describe what actually ships in trunk today.
• Confirm the code-contributions.md Building Installers section reads cleanly with the one-line Linux pointer.
• Confirm the README diff renders correctly on GitHub.

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors? — N/A, docs-only.

[Copilot]

Pull request overview

Updates the Linux-facing documentation to reflect Linux as a supported platform and trims Linux-specific setup details into a dedicated contributor-focused guide.

Changes:

• README: adds Linux to the supported platforms list (with arch hints).
• docs/code-contributions.md: removes the long Linux subsection and replaces it with a pointer to docs/linux.md.
• docs/linux.md: rewrites Linux contributor instructions (source build, desktop entry, URL handler, troubleshooting) and removes outdated/irrelevant sections.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
README.md	Updates supported platforms list to include Linux and adds arch hints.
docs/code-contributions.md	Simplifies installer-building section and points Linux readers to docs/linux.md.
docs/linux.md	Reworks Linux contributor guide; consolidates build + troubleshooting guidance.

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[gavande1]

The changes look good to me. I have one minor comment, but I’m approving anyway.