refactor: extract hooks from App.tsx to improve code health (#62)

Extract vault management (useVaultSwitcher), git history loading
(useGitHistory), dialog state (useDialogs), and keyboard/command
setup (useAppCommands) into dedicated hooks. App.tsx code health
improves from 8.95 to 10.0 — all extracted hooks also score 10.0.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/useVaultSwitcher.ts

@@ -0,0 +1,62 @@
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import { isTauri } from '../mock-tauri'
+import { pickFolder } from '../utils/vault-dialog'
+import type { VaultOption } from '../components/StatusBar'
+
+export const DEFAULT_VAULTS: VaultOption[] = isTauri()
+  ? [
+      { label: 'Demo v2', path: '/Users/luca/Workspace/laputa-app/demo-vault-v2' },
+      { label: 'Laputa', path: '/Users/luca/Laputa' },
+    ]
+  : [
+      { label: 'Demo v2', path: '/Users/luca/Workspace/laputa-app/demo-vault-v2' },
+    ]
+
+interface UseVaultSwitcherOptions {
+  onSwitch: () => void
+  onToast: (msg: string) => void
+}
+
+/** Manages vault path, extra vaults, switching, cloning, and local folder opening. */
+export function useVaultSwitcher({ onSwitch, onToast }: UseVaultSwitcherOptions) {
+  const [vaultPath, setVaultPath] = useState(DEFAULT_VAULTS[0].path)
+  const [extraVaults, setExtraVaults] = useState<VaultOption[]>([])
+  const allVaults = useMemo(() => [...DEFAULT_VAULTS, ...extraVaults], [extraVaults])
+
+  // Refs ensure stable callbacks that always invoke the latest closures,
+  // breaking the circular dependency between useVaultSwitcher and downstream hooks.
+  const onSwitchRef = useRef(onSwitch)
+  const onToastRef = useRef(onToast)
+  useEffect(() => { onSwitchRef.current = onSwitch; onToastRef.current = onToast })
+
+  const addVault = useCallback((path: string, label: string) => {
+    setExtraVaults(prev => prev.some(v => v.path === path) ? prev : [...prev, { label, path }])
+  }, [])
+
+  const switchVault = useCallback((path: string) => {
+    setVaultPath(path)
+    onSwitchRef.current()
+  }, [])
+
+  const handleVaultCloned = useCallback((path: string, label: string) => {
+    addVault(path, label)
+    switchVault(path)
+    onToastRef.current(`Vault "${label}" cloned and opened`)
+  }, [addVault, switchVault])
+
+  const handleOpenLocalFolder = useCallback(async () => {
+    try {
+      const path = await pickFolder('Open vault folder')
+      if (!path) return
+      const label = path.split('/').pop() || 'Local Vault'
+      addVault(path, label)
+      switchVault(path)
+      onToastRef.current(`Vault "${label}" opened`)
+    } catch (err) {
+      console.error('Failed to open local folder:', err)
+      onToastRef.current(`Failed to open folder: ${err}`)
+    }
+  }, [addVault, switchVault])
+
+  return { vaultPath, allVaults, switchVault, handleVaultCloned, handleOpenLocalFolder }
+}