Fix custom theme not applied on startup (light-theme dividers) (#200)

Launching with a custom dark theme left every divider in light-theme colors until you re-toggled the theme in Settings.

`applyTheme` was copy-pasted across the components and the copies drifted. Three of them (+page.svelte's onMount block, AppLayout.svelte, NoteWindow.svelte) had no custom-* branch, so for a custom theme they stripped the dark class and data-theme attribute, matched nothing, and fell back to the bare light :root values.

`+layout.svelte` applied the custom theme correctly, but `AppLayout` — the always-mounted shell — re-runs its own broken copy from an `$effect` on `$theme`, immediately wiping it out. Dividers gave it away because custom themes override `--border-color` but not `--border-light`, which dividers use.

Fix: consolidate into a single `applyTheme`(which already owns darkThemes/isDarkTheme) with a real `custom-*` branch, and have every call site use it and pass the loaded custom themes so `custom-*` ids resolve.

Reviewed-on: https://codeberg.org/ArkHost/HelixNotes/pulls/200

src/lib/components/AppLayout.svelte

@@ -21,6 +21,7 @@
 		showSearch,
 		showCommandPalette,
 		theme,
+		customThemes,
 		focusMode,
 		readOnly,
 		activeNote,
@@ -62,7 +63,7 @@
 	const isMac = navigator.platform.startsWith('Mac');
 	const isMobile = $derived($platformIsMobile);
 	import { loadVaultState, saveVaultState, readNote, createDailyNote, createBackup, getPendingOpenFile, addQuickAccess, removeQuickAccess, getQuickAccess, setTheme, syncNow, setTaskDone, setTaskPriority, setTaskDue, findOrphanedAttachments, trashOrphanedAttachments } from '$lib/api';
-	import { darkThemes, isAndroid } from '$lib/platform';
+	import { applyTheme, isAndroid } from '$lib/platform';
 	import { debounce } from '$lib/utils/debounce';
 	import { openNoteWindow } from '$lib/utils/window';
 	import { get } from 'svelte/store';
@@ -509,21 +510,8 @@
 		}
 	}
 
-	function applyTheme(t: string) {
-		const namedThemes = ['solarized-light', 'solarized-dark', 'catppuccin', 'nord', 'tokyo-night', 'github-light', 'github-dark', 'dracula', 'blueberry', 'forest-green', 'gruvbox', 'midnight-tide', 'cherry-blossom', 'synthwave', 'ember', 'moonlit', 'light-coffee', 'dark-coffee', 'cotton-candy', 'crimson', 'cloud', 'peach', 'material-dark', 'material-light', 'monokai', 'rose-pine', 'everforest', 'horizon', 'cyberpunk', 'black', 'one-dark'];
-		const root = document.documentElement;
-		root.classList.remove('dark');
-		root.removeAttribute('data-theme');
-		if (namedThemes.includes(t)) {
-			root.setAttribute('data-theme', t);
-			if (darkThemes.includes(t)) root.classList.add('dark');
-		} else if (t === 'dark' || (t === 'system' && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
-			root.classList.add('dark');
-		}
-	}
-
 	$effect(() => {
-		applyTheme($theme);
+		applyTheme($theme, $customThemes);
 	});
 
 	$effect(() => {
@@ -605,10 +593,10 @@
 			prefetchPromise = readNote(lastNotePath).catch(() => null);
 		}
 
-		applyTheme($theme);
+		applyTheme($theme, $customThemes);
 
 		window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
-			if ($theme === 'system') applyTheme('system');
+			if ($theme === 'system') applyTheme('system', $customThemes);
 		});
 
 		// Run sidebar and note list refresh in parallel