feat(files): a Files section over the caller's whole space

Until now file browsing existed only inside a project, and the two memory
stores were reachable only by the agent's tools. `#files` is the general
surface: home, both memory stores, the shared folders and projects the
caller belongs to, plus the read-only skills and docs trees.

The root is virtual, and that is the design. Anchoring at `~` is wrong:
the explorer reads host-side, while `shared/`, `projects/`, `skills/` and
`docs/` are bind mounts inside the container — a page rooted at the home
would show less than the user has with no way to reach the rest, and on
native Linux would show Docker's empty mountpoint stubs, a door that
appears to work and leads nowhere. So level 0 is a synthetic list from the
new `GET /api/files/roots`, serialized from the caller's `UserFs` plus the
two virtual memory roots. It sends `kind`, never a label: labels are copy
and get translated.

`GET /api/files/dir` now answers `{ path, can_write, entries }`, and a
memory path is classified before `resolve_view_path` (which refuses one)
and listed from `memory_docs`: one level derived from the flat key space
by the pure `memory_docs::immediate_children`, over a single query whose
unslashed prefix also spots an exact note as "not a directory". Memory is
read-only from the page — every writer routes through `resolve_view_path`,
and `shared-memory/*` is `@fs_write require` for the agent, so a button
that walks past that rule is a decision of its own.

The explorer moves out of projects into `shared/file-explorer.js`, taking
`root` + `rootLabel` and reading `can_write` from the listing rather than
from its host: writability changes per branch and comes from the same
`UserFs::can_write_to` the server rejects writes with, so the buttons
offered and the writes accepted cannot disagree. Deep-linking needed it
steerable without a two-way binding, hence `rel` in and
`explorer-navigate` out — the event fires only for a click, never for a
`rel` the host set, so echoing it back is a no-op.

The URL carries the agent path of the open folder in one parameter, the
same vocabulary the assistant uses, so a link is shareable and pasteable
into a conversation; which root it belongs to is derived, not stored.

docs/: a new files.md, plus two pages this made false — shared-folders.md
claimed in three places that a shared folder has no explorer, and
memory.md never said a user can now read their own notes.

web/i18n/fr.js

@@ -8,6 +8,7 @@ export default {
   'nav.inbox':         'Boîte de réception',
   'nav.dashboard':     'Tableau de bord',
   'nav.projects':      'Projets',
+  'nav.files':         'Fichiers',
   'nav.tasks':         'Gestionnaire de tâches',
   'nav.tasks.running':   'Tâches en cours',
   'nav.tasks.cron':      'Tâches Cron',
@@ -266,26 +267,40 @@ export default {
   'projects.share.access.readwrite':'Lecture et écriture',
   'projects.tabs.files':              'Fichiers',
   'projects.tabs.sharing':            'Partage',
-  'projects.files.col.name':          'Nom',
-  'projects.files.col.created':       'Création',
-  'projects.files.col.modified':      'Modification',
-  'projects.files.col.size':          'Taille',
-  'projects.files.empty':             'Ce dossier est vide.',
-  'projects.files.refresh':           'Actualiser',
-  'projects.files.drop':              'Déposez les fichiers ici pour les envoyer',
-  'projects.files.btn.new_folder':    'Nouveau dossier',
-  'projects.files.btn.upload':        'Envoyer',
-  'projects.files.btn.download':      'Télécharger (ZIP)',
-  'projects.files.uploading':         'Envoi…',
-  'projects.files.action.download':   'Télécharger',
-  'projects.files.action.rename':     'Renommer',
-  'projects.files.action.delete':     'Supprimer',
-  'projects.files.confirm.delete_file': 'Supprimer « {name} » ?',
-  'projects.files.confirm.delete_dir':  'Supprimer le dossier « {name} » et tout son contenu ?',
-  'projects.files.modal.mkdir':       'Nouveau dossier',
-  'projects.files.modal.rename':      'Renommer « {name} »',
-  'projects.files.modal.name':        'Nom',
-  'projects.files.error.name':        'Saisissez un nom valide (sans barres obliques).',
+
+  // ── File explorer (shared component: projects, Files section) ───────────────
+  'files.col.name':          'Nom',
+  'files.col.created':       'Création',
+  'files.col.modified':      'Modification',
+  'files.col.size':          'Taille',
+  'files.empty':             'Ce dossier est vide.',
+  'files.refresh':           'Actualiser',
+  'files.drop':              'Déposez les fichiers ici pour les envoyer',
+  'files.btn.new_folder':    'Nouveau dossier',
+  'files.btn.upload':        'Envoyer',
+  'files.btn.download':      'Télécharger (ZIP)',
+  'files.uploading':         'Envoi…',
+  'files.action.download':   'Télécharger',
+  'files.action.rename':     'Renommer',
+  'files.action.delete':     'Supprimer',
+  'files.confirm.delete_file': 'Supprimer « {name} » ?',
+  'files.confirm.delete_dir':  'Supprimer le dossier « {name} » et tout son contenu ?',
+  'files.modal.mkdir':       'Nouveau dossier',
+  'files.modal.rename':      'Renommer « {name} »',
+  'files.modal.name':        'Nom',
+  'files.error.name':        'Saisissez un nom valide (sans barres obliques).',
+  'files.title':             'Fichiers',
+  'files.note.roots':        'Tout ce que vous pouvez atteindre : votre dossier personnel, vos deux mémoires et les dossiers partagés avec vous. Ce sont les chemins qu\'utilise l\'assistant.',
+  'files.back':              'Tous les fichiers',
+  'files.badge.readonly':    'Lecture seule',
+  'files.error.unknown_path': '« {path} » ne fait pas partie de vos dossiers.',
+  'files.root.home':           'Dossier personnel',
+  'files.root.user_memory':    'Mémoire personnelle',
+  'files.root.shared_memory':  'Mémoire partagée',
+  'files.root.shared':         'Dossier partagé',
+  'files.root.project':        'Projet',
+  'files.root.skills':         'Compétences',
+  'files.root.docs':           'Documentation',
 
   // ── Détail du projet ────────────────────────────────────────────────────────
   'project_board.back':               'Projets',
@@ -1213,6 +1228,7 @@ export default {
   'common.cancel':  'Annuler',
   'common.loading': 'Chargement…',
   'common.saved':   'Enregistré',
+  'common.create':  'Créer',
 
   // ── Shared Folders (blueprint §6) ────────────────────────────────────────────
   'nav.shared_folders':       'Dossiers partagés',