feat(desktop): rebindable keyboard shortcuts panel

Add a central keybind registry + nanostore so desktop hotkeys are
discoverable and user-rebindable. A titlebar ⌨ button (and ⌘/) opens a
collapsible map grouped by Composer (read-only) / Profiles / Session /
Navigation / View; click any chip to capture a new combo. Overrides
persist to localStorage as a delta against shipped defaults, so future
default changes aren't shadowed by a stored snapshot.

Migrates the previously scattered inline listeners (palette, command
center, new session, sidebar, theme) into the registry, and adds profile
switch/cycle/create + default-profile hotkeys.

apps/desktop/src/store/keybinds.ts

@@ -0,0 +1,139 @@
+import { atom, computed } from 'nanostores'
+
+import {
+  defaultBindings,
+  KEYBIND_ACTION_IDS,
+  keybindAction,
+  type KeybindBindings
+} from '@/lib/keybinds/actions'
+import { arraysEqual, persistString, storedString } from '@/lib/storage'
+
+const STORAGE_KEY = 'hermes.desktop.keybinds'
+
+// Defaults overlaid with the user's stored overrides. Unknown / stale action ids
+// are dropped; actions added in a later release pick up their shipped default.
+function loadBindings(): KeybindBindings {
+  const base = defaultBindings()
+  const raw = storedString(STORAGE_KEY)
+
+  if (!raw) {
+    return base
+  }
+
+  try {
+    const parsed = JSON.parse(raw) as Record<string, unknown>
+
+    for (const id of KEYBIND_ACTION_IDS) {
+      const value = parsed[id]
+
+      if (Array.isArray(value)) {
+        base[id] = value.filter((combo): combo is string => typeof combo === 'string')
+      }
+    }
+  } catch {
+    // Corrupt storage falls back to defaults.
+  }
+
+  return base
+}
+
+// Persist only the actions whose combos differ from their shipped default, so
+// changing a default never gets shadowed by a stored snapshot.
+function persistBindings(bindings: KeybindBindings): void {
+  const defaults = defaultBindings()
+  const diff: KeybindBindings = {}
+
+  for (const id of KEYBIND_ACTION_IDS) {
+    const current = bindings[id] ?? []
+
+    if (!arraysEqual(current, defaults[id] ?? [])) {
+      diff[id] = current
+    }
+  }
+
+  persistString(STORAGE_KEY, JSON.stringify(diff))
+}
+
+export const $bindings = atom<KeybindBindings>(loadBindings())
+
+$bindings.subscribe(persistBindings)
+
+// Reverse lookup combo → actionId for dispatch. First action wins on conflict;
+// the panel/edit overlay surface conflicts so users can resolve them.
+export const $comboIndex = computed($bindings, bindings => {
+  const index = new Map<string, string>()
+
+  for (const id of KEYBIND_ACTION_IDS) {
+    for (const combo of bindings[id] ?? []) {
+      if (!index.has(combo)) {
+        index.set(combo, id)
+      }
+    }
+  }
+
+  return index
+})
+
+export function setBinding(actionId: string, combos: string[]): void {
+  if (!keybindAction(actionId)) {
+    return
+  }
+
+  $bindings.set({ ...$bindings.get(), [actionId]: [...combos] })
+}
+
+export function resetBinding(actionId: string): void {
+  const action = keybindAction(actionId)
+
+  if (!action) {
+    return
+  }
+
+  $bindings.set({ ...$bindings.get(), [actionId]: [...action.defaults] })
+}
+
+export function resetAllBindings(): void {
+  $bindings.set(defaultBindings())
+}
+
+// Other actions that already use `combo` (excluding `actionId` itself).
+export function conflictsFor(actionId: string, combo: string): string[] {
+  const bindings = $bindings.get()
+
+  return KEYBIND_ACTION_IDS.filter(id => id !== actionId && (bindings[id] ?? []).includes(combo))
+}
+
+// ── Capture ─────────────────────────────────────────────────────────────────
+// `$capture` is the action currently listening for its next keypress (a panel
+// row armed for rebinding). Session-only — never persisted.
+
+export const $capture = atom<string | null>(null)
+
+export function beginCapture(actionId: string): void {
+  $capture.set(actionId)
+}
+
+export function endCapture(): void {
+  $capture.set(null)
+}
+
+// ── Panel ───────────────────────────────────────────────────────────────────
+
+export const $keybindPanelOpen = atom(false)
+
+export function openKeybindPanel(): void {
+  $keybindPanelOpen.set(true)
+}
+
+export function closeKeybindPanel(): void {
+  $keybindPanelOpen.set(false)
+  $capture.set(null)
+}
+
+export function toggleKeybindPanel(): void {
+  if ($keybindPanelOpen.get()) {
+    closeKeybindPanel()
+  } else {
+    openKeybindPanel()
+  }
+}