fix(plan): make Plán prací usable on mobile + dev port → 3050

Mobile work-plan (Plán prací) responsive fixes — desktop unchanged:
- Toolbar stacks into clean full-width rows on ≤640px (nav group,
  centered range label, full-width segmented view toggle, full-width
  category button); drops the fixed 230px label min-width and the
  margin-left:auto that made the toolbar ragged on phones.
- Grid scroll container: 100dvh-based max-height, momentum scroll, and
  overscroll containment so a fling does not bounce the whole page.
- ≤480px tightens columns (date col 72px via the colgroup <col>, person
  cols 132px) so ~2 people are comfortably visible at 360–390px.
- Touch (@media hover:none): faint persistent + on empty editable
  cells, since the hover-reveal add hint never fires on a phone.

Dev: `npm run dev` (backend) now listens on 3050 instead of 3000 to
avoid colliding with other local apps; CLAUDE.md dev-port note updated.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/PlanWork.tsx

@@ -576,29 +576,35 @@ export default function PlanWork() {
         animate={{ opacity: 1, y: 0 }}
         transition={{ duration: 0.25, delay: 0.12 }}
       >
-        <button
-          type="button"
-          className="admin-btn admin-btn-secondary"
-          onClick={goToToday}
-        >
-          Dnes
-        </button>
-        <button
-          type="button"
-          className="admin-btn admin-btn-secondary"
-          onClick={goPrev}
-          aria-label="Předchozí"
-        >
-          ←
-        </button>
-        <button
-          type="button"
-          className="admin-btn admin-btn-secondary"
-          onClick={goNext}
-          aria-label="Další"
-        >
-          →
-        </button>
+        {/* Nav buttons grouped so they stay on one row when the toolbar
+            stacks on mobile (see .plan-toolbar-nav in plan.css). On desktop
+            the wrapper is an inline-flex with the same 12px gap, so the
+            layout is visually identical. */}
+        <div className="plan-toolbar-nav">
+          <button
+            type="button"
+            className="admin-btn admin-btn-secondary"
+            onClick={goToToday}
+          >
+            Dnes
+          </button>
+          <button
+            type="button"
+            className="admin-btn admin-btn-secondary"
+            onClick={goPrev}
+            aria-label="Předchozí"
+          >
+            ←
+          </button>
+          <button
+            type="button"
+            className="admin-btn admin-btn-secondary"
+            onClick={goNext}
+            aria-label="Další"
+          >
+            →
+          </button>
+        </div>
         <span className="plan-range-label-slot">
           <AnimatePresence mode="popLayout" initial={false}>
             <motion.span
@@ -644,7 +650,7 @@ export default function PlanWork() {
         {canEdit && (
           <button
             type="button"
-            className="admin-btn admin-btn-secondary"
+            className="admin-btn admin-btn-secondary plan-toolbar-cat"
             onClick={() => setCatModalOpen(true)}
           >
             Správa kategorií