feat: Phase 2 feature flags — hide/show sidebar entries per client

- usePhase2Features.js hook: manages localStorage-based feature flags for all 8 Phase 2
  sidebar entries (notes, expenses, contacts, customers, tabs, waste, kds, schedule)
  All default to enabled=true. setFeatureEnabled() writes to localStorage and dispatches
  a 'phase2features' event so all subscribers re-render immediately without page reload
- Phase2FeaturesTab.jsx: new Settings tab 'Λειτουργίες' — toggle each Phase 2 page on/off
  with master 'Ενεργοποίηση όλων' / 'Απενεργοποίηση όλων' buttons
  Note shown: changes are localStorage-only, instant, no reload needed, no data deleted
- SettingsPage.jsx: adds 'Λειτουργίες' and reinstates 'Developer' tab (was missing import)
- Sidebar.jsx: subscribes to phase2features + storage events; filters ALL_NAV to remove
  disabled Phase 2 entries; each phase2 item has a phase2 id that isFeatureEnabled() checks

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

manager_dashboard/src/pages/Settings/tabs/Phase2FeaturesTab.jsx

@@ -0,0 +1,83 @@
+import { PHASE2_FEATURE_DEFS, isFeatureEnabled, setFeatureEnabled, usePhase2Features } from '../../../hooks/usePhase2Features'
+
+function Toggle({ checked, onChange }) {
+  return (
+    <button
+      role="switch"
+      aria-checked={checked}
+      onClick={() => onChange(!checked)}
+      style={{
+        width: 44, height: 24, borderRadius: 999, border: 'none', cursor: 'pointer',
+        background: checked ? '#16a34a' : '#d1d5db',
+        position: 'relative', transition: 'background 150ms', flexShrink: 0,
+      }}
+    >
+      <span style={{
+        position: 'absolute', top: 3, left: checked ? 23 : 3,
+        width: 18, height: 18, borderRadius: '50%', background: 'white',
+        transition: 'left 150ms', boxShadow: '0 1px 3px rgba(0,0,0,0.2)',
+      }} />
+    </button>
+  )
+}
+
+export default function Phase2FeaturesTab() {
+  const features = usePhase2Features()
+
+  const allOn  = features.every(f => f.enabled)
+  const allOff = features.every(f => !f.enabled)
+
+  function toggleAll(value) {
+    PHASE2_FEATURE_DEFS.forEach(f => setFeatureEnabled(f.id, value))
+  }
+
+  return (
+    <div className="space-y-4 max-w-xl">
+      <div className="rounded-lg border border-blue-200 bg-blue-50 px-4 py-3 text-xs text-blue-800">
+        Αυτές οι επιλογές ελέγχουν ποιες σελίδες Phase 2 εμφανίζονται στο πλαϊνό μενού.
+        Απενεργοποίηση <strong>δεν σβήνει δεδομένα</strong> — απλώς κρύβει τον σύνδεσμο.
+        Χρήσιμο για να κρατάτε σελίδες σε εξέλιξη κρυφές από πελάτες.
+      </div>
+
+      <div className="card divide-y divide-gray-100">
+        {/* Master toggle row */}
+        <div className="flex items-center justify-between gap-4 px-5 py-3 bg-gray-50/60">
+          <span className="text-sm font-semibold text-gray-600">Όλες οι λειτουργίες</span>
+          <div className="flex gap-3">
+            <button
+              onClick={() => toggleAll(true)}
+              disabled={allOn}
+              className="text-xs font-semibold px-3 py-1 rounded-full border border-green-300 text-green-700 hover:bg-green-50 disabled:opacity-40 disabled:cursor-default"
+            >
+              Ενεργοποίηση όλων
+            </button>
+            <button
+              onClick={() => toggleAll(false)}
+              disabled={allOff}
+              className="text-xs font-semibold px-3 py-1 rounded-full border border-red-300 text-red-600 hover:bg-red-50 disabled:opacity-40 disabled:cursor-default"
+            >
+              Απενεργοποίηση όλων
+            </button>
+          </div>
+        </div>
+
+        {features.map(f => (
+          <div key={f.id} className="flex items-center justify-between gap-4 px-5 py-3">
+            <div>
+              <p className="text-sm font-medium text-gray-700">{f.label}</p>
+              <p className="text-xs text-gray-400 mt-0.5 font-mono">{f.route}</p>
+            </div>
+            <Toggle
+              checked={f.enabled}
+              onChange={val => setFeatureEnabled(f.id, val)}
+            />
+          </div>
+        ))}
+      </div>
+
+      <p className="text-xs text-gray-400">
+        Οι ρυθμίσεις αποθηκεύονται τοπικά στον browser. Ισχύουν αμέσως χωρίς ανανέωση.
+      </p>
+    </div>
+  )
+}