Fix Qwen provider preference reset after refresh

[Manho]

Summary

• preserve synced Qwen provider preferences when optional host permission is missing on the current device
• keep device-local content scripts and frame rules aligned with locally granted permissions
• prevent unavailable Qwen providers from loading while allowing the settings page to request access again
• add unit and browser regression coverage for the enable-and-refresh production failure

Root cause

The background reconciliation flow treated device-local optional host permission as the source of truth for the synced enabledProviders preference. A permission mismatch could therefore remove Qwen from chrome.storage.sync, causing the provider toggle to turn off after the setting propagated or the page refreshed.

Impact

Qwen preferences now remain stable across refreshes and synced browsers. Devices without local permission keep the preference without loading an inaccessible panel, and users can grant access from the settings page without accidentally disabling Qwen.

Validation

• npx vitest run --exclude 'tests/e2e/**' — 249 tests passed
• npx playwright test tests/e2e --reporter=dot — 30 tests passed
• JavaScript syntax checks passed for all modified source and regression test files
• git diff --check passed
• settings page visually verified from the new browser regression test screenshot