feat(filebrowser): add toggle to show/hide hidden files and .env synt…

[NeonPimpZ]

What does this PR do?

• Show/hide hidden files toggle — adds an eye icon button to the file browser toolbar. When enabled, files and folders whose names begin with . are shown alongside regular files. The toggle state is stored in Vuex (showHiddenFiles) so it persists across navigation within the session. Off by default to preserve existing behaviour.
• .env syntax highlighting — the code editor now detects files named .env or matching .env.* and applies shell (text/x-sh) syntax highlighting, making environment files easier to read and edit.

Test plan

• Open the file browser — hidden files (e.g. .gitignore, .env) should not appear by default
• Click the eye toggle in the toolbar — hidden files should appear; click again to hide them
• Open a .env file in the code editor — verify syntax highlighting is applied

Related Issue

IceWhaleTech/CasaOS#1848

[sonarqubecloud]

Quality Gate failed

Failed conditions
B Reliability Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

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