feat: partage dirigé entre utilisateurs #196

- create_share/shared_with + validation des destinataires
- gate auth sur /s/{token} (+pdf, raw) : 404 opaque hors créateur/admin/destinataires
- GET /api/shares scopé (non-admin = créés + reçus), révocation créateur/admin
- UI : dialogue dirigé/public + destinataires, dashboard « partagé par X »
- i18n FR/EN, tests test_directed_shares.py (9), fiche feature

frontend/locales/en.json

@@ -604,6 +604,11 @@
   "config.server_config": "Server config",
   "config.settings_saved": "✓ Settings saved",
   "config.share_revoked": "Share revoked",
+  "config.share_directed": "Share with users (authentication required)",
+  "config.share_public": "Public link (no authentication)",
+  "config.share_recipients_ph": "Recipients (usernames, comma-separated)",
+  "config.share_need_recipient": "Provide at least one recipient",
+  "config.share_shared_with": "Shared with",
   "config.shares": "Public shares",
   "config.shares_desc": "Manage public share links for your documents.",
   "config.shares_empty": "No active shares",
@@ -701,6 +706,7 @@
   "dashboard.recent": "Recent",
   "dashboard.recent_hint": "Open a file to see it appear here",
   "dashboard.shared_hint": "Share a document to see it appear here",
+  "dashboard.shared_by": "Shared by {user}",
   "dashboard.shares": "Shares",
   "dashboard.show": "Show",
   "dashboard.size_bytes": " B",