feat(nav): bouton action intégré dans la navbar v0.4.8

- ActionButtonContext : contexte React permettant aux pages d'injecter
  leur bouton action dans la navbar (Shopping=fa-cart-plus, Todos/Notes=+)
- BottomNav : 5e slot dédié avec dock circulaire visuel permanent ;
  bouton rendu 10px au-dessus du centre du slot (effet soulevé)
- Layout : ActionButtonProvider + overflow visible sur le conteneur nav
- Pages : useEffect enregistre/vide le bouton action — plus de FAB flottant
  sur le contenu, liste entièrement visible

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

frontend/src/pages/NotesPage.tsx

@@ -3,6 +3,7 @@ import type { Note, NoteFilters } from '../api/notes'
 import { fetchNotes, createNote, updateNote, deleteNote, addAttachment, deleteAttachment } from '../api/notes'
 import Modal from '../components/Modal'
 import NoteForm from '../components/notes/NoteForm'
+import { useActionButton } from '../contexts/ActionButtonContext'
 
 const noSelect: React.CSSProperties = { userSelect: 'none' }
 
@@ -163,6 +164,24 @@ export default function NotesPage() {
   const [searchInput, setSearchInput] = useState('')
   const searchTimer = useRef<ReturnType<typeof setTimeout> | null>(null)
 
+  const { setActionButton } = useActionButton()
+  useEffect(() => {
+    setActionButton(
+      <button
+        onClick={() => setShowForm(true)}
+        aria-label="Nouvelle note"
+        style={{
+          width: 56, height: 56, borderRadius: '50%',
+          background: 'var(--accent)', color: '#1d2021', border: 'none',
+          fontSize: 24, cursor: 'pointer',
+          boxShadow: '0 4px 16px rgba(0,0,0,0.5)',
+          display: 'flex', alignItems: 'center', justifyContent: 'center',
+        }}
+      >+</button>
+    )
+    return () => setActionButton(null)
+  }, [setActionButton])
+
   const load = useCallback(async () => {
     setLoading(true)
     setError(null)
@@ -348,20 +367,6 @@ export default function NotesPage() {
         </div>
       </div>
 
-      {/* FAB */}
-      <button
-        className="fixed bottom-[10px] right-3 lg:bottom-6 lg:right-6"
-        onClick={() => setShowForm(true)}
-        aria-label="Nouvelle note"
-        style={{
-          width: 56, height: 56, borderRadius: '50%',
-          background: 'var(--accent)', color: '#1d2021',
-          border: 'none', fontSize: 28, cursor: 'pointer',
-          boxShadow: '0 4px 12px rgba(0,0,0,0.5)',
-          display: 'flex', alignItems: 'center', justifyContent: 'center',
-          lineHeight: 1,
-        }}
-      >+</button>
     </div>
   )
 }

frontend/src/pages/ShoppingPage.tsx

@@ -1,5 +1,5 @@
 // frontend/src/pages/ShoppingPage.tsx
-import { useState, useEffect, useCallback } from 'react'
+import { useState, useEffect, useCallback, useRef } from 'react'
 import { matchesSearch } from '../utils/search'
 import type { ShoppingListDetail, ShoppingList, Store, Product, ShoppingItem } from '../api/shopping'
 import {
@@ -13,6 +13,7 @@ import ItemRow from '../components/shopping/ItemRow'
 import CatalogueModal from '../components/shopping/CatalogueModal'
 import BoutiquesModal from '../components/shopping/BoutiquesModal'
 import { useWakeLock } from '../hooks/useWakeLock'
+import { useActionButton } from '../contexts/ActionButtonContext'
 
 const inputStyle: React.CSSProperties = {
   width: '100%',
@@ -76,6 +77,33 @@ export default function ShoppingPage() {
 
   useWakeLock(currentList !== null)
 
+  const { setActionButton } = useActionButton()
+  const openAddSheetRef = useRef(openAddSheet)
+  useEffect(() => { openAddSheetRef.current = openAddSheet })
+
+  useEffect(() => {
+    if (!currentList || showAddSheet) {
+      setActionButton(null)
+      return
+    }
+    setActionButton(
+      <button
+        onClick={() => openAddSheetRef.current()}
+        aria-label="Ajouter un article"
+        style={{
+          width: 56, height: 56, borderRadius: '50%',
+          background: 'var(--accent)', color: '#1d2021', border: 'none',
+          fontSize: 22, cursor: 'pointer',
+          boxShadow: '0 4px 16px rgba(0,0,0,0.5)',
+          display: 'flex', alignItems: 'center', justifyContent: 'center',
+        }}
+      >
+        <i className="fa-solid fa-cart-plus" />
+      </button>
+    )
+    return () => setActionButton(null)
+  }, [currentList, showAddSheet, setActionButton])
+
   const loadData = useCallback(async () => {
     setLoading(true)
     setError(null)
@@ -526,22 +554,6 @@ export default function ShoppingPage() {
             )}
           </div>
 
-          {/* FAB — masqué quand le sheet est ouvert */}
-          {!showAddSheet && (
-            <button
-              onClick={openAddSheet}
-              aria-label="Ajouter un article"
-              style={{
-                position: 'fixed', bottom: 10, right: 12,
-                width: 56, height: 56, borderRadius: '50%',
-                background: 'var(--accent)', color: '#1d2021', border: 'none',
-                fontSize: 22, cursor: 'pointer', boxShadow: '0 4px 12px rgba(0,0,0,0.5)',
-                display: 'flex', alignItems: 'center', justifyContent: 'center',
-              }}
-            >
-              <i className="fa-solid fa-cart-plus" />
-            </button>
-          )}
         </>
       )}
 

frontend/src/pages/TodosPage.tsx

@@ -5,6 +5,7 @@ import { fetchTodos, createTodo, updateTodo, deleteTodo, postponeTodo } from '..
 import SwipeableRow from '../components/todos/SwipeableRow'
 import TodoForm, { DOMAIN_COLORS } from '../components/todos/TodoForm'
 import Modal from '../components/Modal'
+import { useActionButton } from '../contexts/ActionButtonContext'
 
 type EditingTodo = Todo | null
 
@@ -41,6 +42,24 @@ export default function TodosPage() {
   const [editingTodo, setEditingTodo] = useState<EditingTodo>(null)
   const [filters, setFilters] = useState<TodoFilters>({ status: 'pending' })
 
+  const { setActionButton } = useActionButton()
+  useEffect(() => {
+    setActionButton(
+      <button
+        onClick={() => setShowForm(true)}
+        aria-label="Nouvelle tâche"
+        style={{
+          width: 56, height: 56, borderRadius: '50%',
+          background: 'var(--accent)', color: '#1d2021', border: 'none',
+          fontSize: 24, cursor: 'pointer',
+          boxShadow: '0 4px 16px rgba(0,0,0,0.5)',
+          display: 'flex', alignItems: 'center', justifyContent: 'center',
+        }}
+      >+</button>
+    )
+    return () => setActionButton(null)
+  }, [setActionButton])
+
   const load = useCallback(async () => {
     setLoading(true)
     setError(null)
@@ -395,27 +414,6 @@ export default function TodosPage() {
         )}
       </div>
 
-      {/* FAB création — mobile : au-dessus de la barre de nav ; laptop : coin bas-droit */}
-      <button
-        className="fixed bottom-[10px] right-3 lg:bottom-6 lg:right-6"
-        onClick={() => setShowForm(true)}
-        aria-label="Nouvelle tâche"
-        style={{
-          width: 56,
-          height: 56,
-          borderRadius: '50%',
-          background: 'var(--accent)',
-          color: '#1d2021',
-          border: 'none',
-          fontSize: 28,
-          cursor: 'pointer',
-          boxShadow: '0 4px 12px rgba(0,0,0,0.5)',
-          display: 'flex',
-          alignItems: 'center',
-          justifyContent: 'center',
-          lineHeight: 1,
-        }}
-      >+</button>
     </div>
   )
 }