feat(keybindings): in-app modifier chords; fix seek shortcut units

Persist chords as ctrl/alt/shift/super plus key code; legacy single-key
bindings still match without modifiers. Settings capture uses buildInAppBinding;
App uses matchInAppBinding and skips chords also registered as global shortcuts.
Share MODIFIER_KEY_CODES and formatBinding with global shortcut formatting.

Fix seek-forward/backward hotkeys: seek() expects 0-1 progress, not seconds.

src/store/globalShortcutsStore.ts

@@ -1,18 +1,13 @@
 import { create } from 'zustand';
 import { persist } from 'zustand/middleware';
 import { invoke } from '@tauri-apps/api/core';
-import { formatKeyCode } from './keybindingsStore';
+import { MODIFIER_KEY_CODES, formatBinding } from './keybindingsStore';
 
 export type GlobalAction = 'play-pause' | 'next' | 'prev' | 'volume-up' | 'volume-down';
 
-const MODIFIER_CODES = [
-  'ControlLeft', 'ControlRight', 'AltLeft', 'AltRight',
-  'ShiftLeft', 'ShiftRight', 'MetaLeft', 'MetaRight', 'OSLeft', 'OSRight',
-];
-
 /** Build a Tauri-compatible shortcut string from a KeyboardEvent, or null if invalid. */
 export function buildGlobalShortcut(e: KeyboardEvent): string | null {
-  if (MODIFIER_CODES.includes(e.code)) return null;
+  if ((MODIFIER_KEY_CODES as readonly string[]).includes(e.code)) return null;
   // Require at least Ctrl, Alt, or Meta — Shift alone is too invasive
   if (!e.ctrlKey && !e.altKey && !e.metaKey) return null;
 
@@ -27,13 +22,7 @@ export function buildGlobalShortcut(e: KeyboardEvent): string | null {
 
 /** Human-readable label for a stored shortcut string, e.g. "ctrl+alt+ArrowRight" → "Ctrl+Alt+→". */
 export function formatGlobalShortcut(shortcut: string): string {
-  return shortcut.split('+').map(part => {
-    if (part === 'ctrl')  return 'Ctrl';
-    if (part === 'alt')   return 'Alt';
-    if (part === 'shift') return 'Shift';
-    if (part === 'super' || part === 'meta') return 'Super';
-    return formatKeyCode(part);
-  }).join('+');
+  return formatBinding(shortcut);
 }
 
 // Module-level guard — prevents double-registration from React StrictMode's

src/store/keybindingsStore.ts

@@ -14,7 +14,13 @@ export type KeyAction =
   | 'fullscreen-player'
   | 'native-fullscreen';
 
-// key = action, value = e.code string (e.g. 'Space', 'KeyN', 'F11') or null for unbound
+/** Physical keys only — ignore for binding capture */
+export const MODIFIER_KEY_CODES = [
+  'ControlLeft', 'ControlRight', 'AltLeft', 'AltRight',
+  'ShiftLeft', 'ShiftRight', 'MetaLeft', 'MetaRight', 'OSLeft', 'OSRight',
+] as const;
+
+// key = action, value = plain e.code ("Space", "KeyN") or chord "ctrl+shift+KeyN", null = unbound
 export type Bindings = Record<KeyAction, string | null>;
 
 export const DEFAULT_BINDINGS: Bindings = {
@@ -33,16 +39,49 @@ export const DEFAULT_BINDINGS: Bindings = {
 
 interface KeybindingsState {
   bindings: Bindings;
-  setBinding: (action: KeyAction, code: string | null) => void;
+  setBinding: (action: KeyAction, binding: string | null) => void;
   resetToDefaults: () => void;
 }
 
+/** Build persisted binding from a keydown: single key or modifier+key chord. */
+export function buildInAppBinding(e: KeyboardEvent): string | null {
+  if ((MODIFIER_KEY_CODES as readonly string[]).includes(e.code)) return null;
+  if (!e.ctrlKey && !e.altKey && !e.shiftKey && !e.metaKey) return e.code;
+  const mods: string[] = [];
+  if (e.ctrlKey) mods.push('ctrl');
+  if (e.altKey) mods.push('alt');
+  if (e.shiftKey) mods.push('shift');
+  if (e.metaKey) mods.push('super');
+  return [...mods, e.code].join('+');
+}
+
+/** True if the event matches a stored binding (legacy plain codes = no modifiers). */
+export function matchInAppBinding(e: KeyboardEvent, binding: string | null): boolean {
+  if (!binding) return false;
+  if (!binding.includes('+')) {
+    return (
+      e.code === binding &&
+      !e.ctrlKey && !e.altKey && !e.shiftKey && !e.metaKey
+    );
+  }
+  const parts = binding.split('+');
+  const code = parts[parts.length - 1];
+  if (e.code !== code) return false;
+  const mods = new Set(parts.slice(0, -1));
+  return (
+    e.ctrlKey === mods.has('ctrl') &&
+    e.altKey === mods.has('alt') &&
+    e.shiftKey === mods.has('shift') &&
+    e.metaKey === mods.has('super')
+  );
+}
+
 export const useKeybindingsStore = create<KeybindingsState>()(
   persist(
     (set) => ({
       bindings: { ...DEFAULT_BINDINGS },
-      setBinding: (action, code) =>
-        set(s => ({ bindings: { ...s.bindings, [action]: code } })),
+      setBinding: (action, binding) =>
+        set(s => ({ bindings: { ...s.bindings, [action]: binding } })),
       resetToDefaults: () => set({ bindings: { ...DEFAULT_BINDINGS } }),
     }),
     { name: 'psysonic_keybindings' }
@@ -80,3 +119,15 @@ export function formatKeyCode(code: string): string {
   if (code === 'Slash') return '/';
   return code;
 }
+
+/** Label for settings UI: plain key or chord (same string shape as global shortcuts). */
+export function formatBinding(binding: string): string {
+  if (!binding.includes('+')) return formatKeyCode(binding);
+  return binding.split('+').map(part => {
+    if (part === 'ctrl') return 'Ctrl';
+    if (part === 'alt') return 'Alt';
+    if (part === 'shift') return 'Shift';
+    if (part === 'super' || part === 'meta') return 'Super';
+    return formatKeyCode(part);
+  }).join('+');
+}