fix: popout theme inheritance via URL query param

- Pass current theme as ?theme=dark|light in popout URL
- viewer.js, app.js, palette.js all pass theme to popout
- popout.html reads theme from URL param first (fallback: localStorage, then dark)
- Also syncs theme back to localStorage when set via query param

frontend/js/palette.js

@@ -40,7 +40,7 @@ function getCMDS() {
   _cmdsCache = [
   { id:'home',         label:t('palette.cmd_back_home'),      desc:t('palette.cmd_back_home_desc'),   cat:'Navigation',  act:()=>{close();triggerGoHome();} },
   { id:'edit-current', label:'✏️ '+t('editor.edit'),           desc:t('editor.edit_current_desc'),      cat:'Fichiers', act:()=>{close();const f=getCurrentFile();if(f)openEditor(f.vault,f.path);else showToast(t('toast.no_open_file'),'error');} },
-  { id:'popout',       label:'🪟 Pop-out',                    desc:t('palette.popout_desc'),            cat:'Fichiers',  act:()=>{close();const f=getCurrentFile();if(f)window.open(`/popout/${encodeURIComponent(f.vault)}/${encodeURIComponent(f.path)}`,'popout','width=1000,height=700');else showToast(t('toast.no_open_file'),'error');} },
+  { id:'popout',       label:'🪟 Pop-out',                    desc:t('palette.popout_desc'),            cat:'Fichiers',  act:()=>{close();const f=getCurrentFile();if(f)window.open(`/popout/${encodeURIComponent(f.vault)}/${encodeURIComponent(f.path)}?theme=${document.documentElement.getAttribute('data-theme')||'dark'}`,'popout','width=1000,height=700');else showToast(t('toast.no_open_file'),'error');} },
   { id:'create-file',  label:t('palette.cmd_create_file'),     desc:t('palette.cmd_create_file_desc'),   cat:'Fichiers', act:()=>startBrowse('create-file') },
   { id:'delete-file',  label:'🗑️ '+t('file.delete'),            desc:t('palette.delete_file_desc'),    cat:'Fichiers', act:()=>startBrowse('delete-file') },
   { id:'delete-cur',   label:'🗑️ '+t('palette.delete_current'), desc:t('palette.delete_current_desc'), cat:'Fichiers', act:async()=>{close();await delCurFile();} },