projects: file explorer, ws improvements, i18n, and fs routing

Add project-files component with tree navigation. Extend UserFs with
shared-folder resolution. Wire API routes for file browsing. Improve
WS session lifecycle and project-board layout. Add i18n keys for
projects and inbox across all locales.

web/i18n/en.js

@@ -221,7 +221,26 @@ export default {
   'projects.share.access.write':    'Write',
   'projects.share.access.readonly': 'Read-only',
   'projects.share.access.readwrite':'Read & write',
-  'projects.files.placeholder':     'The project files live here. Open the chat to work in this folder — a file explorer is coming.',
+  'projects.tabs.files':              'Files',
+  'projects.tabs.sharing':            'Sharing',
+  'projects.files.col.name':          'Name',
+  'projects.files.col.created':       'Created',
+  'projects.files.col.modified':      'Modified',
+  'projects.files.col.size':          'Size',
+  'projects.files.empty':             'This folder is empty.',
+  'projects.files.refresh':           'Refresh',
+  'projects.files.drop':              'Drop files here to upload',
+  'projects.files.btn.new_folder':    'New folder',
+  'projects.files.btn.upload':        'Upload',
+  'projects.files.uploading':         'Uploading…',
+  'projects.files.action.rename':     'Rename',
+  'projects.files.action.delete':     'Delete',
+  'projects.files.confirm.delete_file': 'Delete "{name}"?',
+  'projects.files.confirm.delete_dir':  'Delete the folder "{name}" and everything inside it?',
+  'projects.files.modal.mkdir':       'New folder',
+  'projects.files.modal.rename':      'Rename "{name}"',
+  'projects.files.modal.name':        'Name',
+  'projects.files.error.name':        'Enter a valid name (no slashes).',
 
   // ── Project detail ──────────────────────────────────────────────────────────
   'project_board.back':               'Projects',

web/i18n/fr.js

@@ -221,7 +221,26 @@ export default {
   'projects.share.access.write':    'Écriture',
   'projects.share.access.readonly': 'Lecture seule',
   'projects.share.access.readwrite':'Lecture et écriture',
-  'projects.files.placeholder':     'Les fichiers du projet vivent ici. Ouvrez la discussion pour travailler dans ce dossier — un explorateur de fichiers arrive bientôt.',
+  '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.uploading':         'Envoi…',
+  '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).',
 
   // ── Détail du projet ────────────────────────────────────────────────────────
   'project_board.back':               'Projets',

web/i18n/it.js

@@ -245,7 +245,26 @@ export default {
   'projects.share.access.write':    'Scrittura',
   'projects.share.access.readonly': 'Sola lettura',
   'projects.share.access.readwrite':'Lettura e scrittura',
-  'projects.files.placeholder':     'Qui vivono i file del progetto. Apri la chat per lavorare in questa cartella — un file explorer è in arrivo.',
+  'projects.tabs.files':              'File',
+  'projects.tabs.sharing':            'Condivisione',
+  'projects.files.col.name':          'Nome',
+  'projects.files.col.created':       'Creazione',
+  'projects.files.col.modified':      'Ultima modifica',
+  'projects.files.col.size':          'Dimensione',
+  'projects.files.empty':             'Questa cartella è vuota.',
+  'projects.files.refresh':           'Aggiorna',
+  'projects.files.drop':              'Trascina qui i file per caricarli',
+  'projects.files.btn.new_folder':    'Nuova cartella',
+  'projects.files.btn.upload':        'Carica',
+  'projects.files.uploading':         'Caricamento…',
+  'projects.files.action.rename':     'Rinomina',
+  'projects.files.action.delete':     'Elimina',
+  'projects.files.confirm.delete_file': 'Eliminare "{name}"?',
+  'projects.files.confirm.delete_dir':  'Eliminare la cartella "{name}" e tutto il suo contenuto?',
+  'projects.files.modal.mkdir':       'Nuova cartella',
+  'projects.files.modal.rename':      'Rinomina "{name}"',
+  'projects.files.modal.name':        'Nome',
+  'projects.files.error.name':        'Inserisci un nome valido (senza barre).',
 
   // ── Dettaglio progetto ──────────────────────────────────────────────────────
   'project_board.back':               'Progetti',