feat: add preset configurations with built-in and custom presets

Add preset store with three built-in presets (Strict mode, Research only,
Full access) and localStorage persistence for custom presets. Integrate
preset selector into ConfigSidebar with load, save, and delete actions.
Built-in presets cannot be deleted.

Closes #14

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/lib/stores/presets.svelte.ts

@@ -0,0 +1,116 @@
+import { OverrideLevel } from '$lib/proto/llm_multiverse/v1/common_pb';
+
+export interface PresetConfig {
+	overrideLevel: OverrideLevel;
+	disabledTools: string[];
+	grantedPermissions: string[];
+}
+
+export interface Preset {
+	name: string;
+	config: PresetConfig;
+	builtIn: boolean;
+}
+
+const STORAGE_KEY = 'llm-multiverse-presets';
+
+const builtInPresets: Preset[] = [
+	{
+		name: 'Strict mode',
+		config: {
+			overrideLevel: OverrideLevel.NONE,
+			disabledTools: ['FS Write', 'Run Shell', 'Run Code', 'Package Install'],
+			grantedPermissions: []
+		},
+		builtIn: true
+	},
+	{
+		name: 'Research only',
+		config: {
+			overrideLevel: OverrideLevel.NONE,
+			disabledTools: ['Memory Write', 'FS Write', 'Run Code', 'Run Shell', 'Package Install'],
+			grantedPermissions: []
+		},
+		builtIn: true
+	},
+	{
+		name: 'Full access',
+		config: {
+			overrideLevel: OverrideLevel.ALL,
+			disabledTools: [],
+			grantedPermissions: []
+		},
+		builtIn: true
+	}
+];
+
+function loadCustomPresets(): Preset[] {
+	if (typeof localStorage === 'undefined') return [];
+	try {
+		const raw = localStorage.getItem(STORAGE_KEY);
+		if (!raw) return [];
+		const parsed: Preset[] = JSON.parse(raw);
+		return parsed.map((p) => ({ ...p, builtIn: false }));
+	} catch {
+		return [];
+	}
+}
+
+function saveCustomPresets(presets: Preset[]) {
+	if (typeof localStorage === 'undefined') return;
+	const custom = presets.filter((p) => !p.builtIn);
+	localStorage.setItem(STORAGE_KEY, JSON.stringify(custom));
+}
+
+function createPresetStore() {
+	const customPresets = $state<Preset[]>(loadCustomPresets());
+
+	function getAllPresets(): Preset[] {
+		return [...builtInPresets, ...customPresets];
+	}
+
+	function savePreset(name: string, config: PresetConfig): Preset {
+		const trimmed = name.trim();
+		if (!trimmed) throw new Error('Preset name cannot be empty');
+		if (builtInPresets.some((p) => p.name === trimmed)) {
+			throw new Error('Cannot overwrite a built-in preset');
+		}
+
+		const existing = customPresets.findIndex((p) => p.name === trimmed);
+		const preset: Preset = { name: trimmed, config, builtIn: false };
+
+		if (existing >= 0) {
+			customPresets[existing] = preset;
+		} else {
+			customPresets.push(preset);
+		}
+
+		saveCustomPresets(customPresets);
+		return preset;
+	}
+
+	function loadPreset(name: string): PresetConfig | null {
+		const all = getAllPresets();
+		const preset = all.find((p) => p.name === name);
+		return preset?.config ?? null;
+	}
+
+	function deletePreset(name: string): boolean {
+		if (builtInPresets.some((p) => p.name === name)) return false;
+		const idx = customPresets.findIndex((p) => p.name === name);
+		if (idx < 0) return false;
+
+		customPresets.splice(idx, 1);
+		saveCustomPresets(customPresets);
+		return true;
+	}
+
+	return {
+		getAllPresets,
+		savePreset,
+		loadPreset,
+		deletePreset
+	};
+}
+
+export const presetStore = createPresetStore();