fix(linux): use solid surfaces for windows

[H-Chris233]

User description

Summary

• Disable transparent Linux windows for main, capsule, and QA so WebKitGTK compositing no longer controls the window background.
• Route Linux shell/frost surfaces to opaque var(--ol-surface) styling while preserving macOS/Windows glass behavior.
• Remove the obsolete is_no_compositing_mode frontend fallback command and CSS path.

Test Plan

• git diff --check
• git diff --cached --check
• node -e "const fs=require('fs'); const cfg=JSON.parse(fs.readFileSync('openless-all/app/src-tauri/tauri.linux.conf.json','utf8')); for (const w of cfg.app.windows) { if (w.transparent !== false) throw new Error(w.label + ' transparent is not false'); } console.log('linux windows transparent=false:', cfg.app.windows.map(w=>w.label).join(', '));"
• npm --prefix "openless-all/app" run build
• cargo check --manifest-path "openless-all/app/src-tauri/Cargo.toml"

Refs #553

Note: Linux GUI visual verification is still needed for the original hover/refresh symptom.

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PR Type

Bug fix

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Description

• Use opaque surfaces for Linux windows

• Remove no-compositing frontend fallback

• Add platform-specific CSS for solid backgrounds

• Fix frosted glass flicker on hover/resize

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Diagram Walkthrough

flowchart LR
  A["Transparent Linux windows (compositing)"]
  B["CSS glass effect with backdrop-filter"]
  C["Flicker on hover/resize due to WebKitGTK"]
  D["Set transparent:false in tauri.linux.conf.json"]
  E["Remove is_no_compositing_mode fallback"]
  F["Use var(--ol-surface) opaque background on Linux"]
  G["Stable solid background without flicker"]
  A -- "leads to" --> C
  D -- "disables" --> A
  E -- "removes" --> B
  F -- "replaced by" --> B
  C -- "fixed by" --> G
  D --> G
  E --> G
  F --> G

Loading

File Walkthrough

	Relevant files
Bug fix	3 files commands.rs Remove is_no_compositing_mode command                                        +0/-6      lib.rs Unregister is_no_compositing_mode command                                +0/-1      App.tsx Remove is_no_compositing_mode invocation                                  +0/-14
Documentation	2 files Capsule.tsx Update comment for Linux solid surface                                      +1/-1      QaPanel.tsx Update comment for Linux platform                                                +2/-3
Enhancement	4 files FloatingShell.tsx Use opaque background on Linux                                                      +4/-7      WindowChrome.tsx Use solid surface on Linux                                                              +9/-11    main.tsx Add platform detection for CSS targeting                                  +4/-1      global.css Add Linux-specific solid background rules                                +11/-47
Configuration changes	1 files tauri.linux.conf.json Disable transparent windows on Linux                                          +3/-3

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[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

🎫 Ticket compliance analysis ✅ 553 - PR Code Verified Compliant requirements: The PR disables transparent windows on Linux and uses solid surfaces, eliminating the WebKit compositing instability that caused the glass effect to flicker/disappear. Requires further human verification: Visual verification of the fix on Linux (as noted in the PR description).

⏱️ Estimated effort to review: 2 🔵🔵⚪⚪⚪

🧪 No relevant tests

🔒 No security concerns identified

⚡ No major issues detected