Projects: shareable, registry-backed, container-mounted; drop ticket board

Rework projects from single-user leftovers into shareable endeavours.

- DB: move `projects` from the owner bucket to the registry (system.db,
  not encrypted); add `owner_user_id` + `slug` (drop free `path`); new
  `project_members(project_id, user_id, can_write)` mirroring
  `shared_folder_members`. Drop `project_tickets` entirely. Only user↔agent
  conversations stay encrypted (per-user DB) — each member keeps a private
  project chat. Registry home dissolves the cross-DB-FK problem.
- Filesystem/container: on disk `{WD}/projects/{owner_userid}/{slug}`,
  agent/container path `projects/{owner_username}/{slug}`. Two-segment routing
  in UserFs (ProjectMount + host_base_and_tail arm) and a second loop in
  build_user_fs; read-only members get a :ro mount. Reuse the shared-folder
  remount machinery (refresh_user_shared_folders -> refresh_user_mounts).
- Remove the ticket system: ProjectTicketManager, UserContext.tickets, its
  wiring, and the project_tickets references in scheduled_jobs/cron.
- API: repoint handlers to the registry pool + membership scoping. Sharing is
  self-service — owner or any write-member may add/remove members and set
  read/write; only the owner deletes; the owner cannot be removed. New
  POST/DELETE /api/projects/{id}/members[/{user_id}]. Seed `@fs_any allow
  projects/*`; build_runtime_run_context sets working_directory to the agent
  path and drops the host-path allow_fs_writes.
- Frontend: create form without the free path field, owner/read-write badges;
  the detail page becomes header + description + sharing panel + Open chat + a
  file-explorer placeholder (the future primary surface). i18n en/it/fr.

web/i18n/en.js

@@ -184,14 +184,15 @@ export default {
   'projects.action.edit':           'Edit',
   'projects.action.delete':         'Delete',
   'projects.card.updated':          'Updated',
-  'projects.confirm.delete':        'Delete project "{name}"?\nAll tickets will also be deleted.',
+  'projects.confirm.delete':        'Delete project "{name}"? This removes it for everyone it is shared with.',
+  'projects.badge.owned':           'Owned',
+  'projects.badge.shared_by':       'Shared by {name}',
+  'projects.badge.readonly':        'Read-only',
 
   'projects.modal.title_edit':      'Edit Project',
   'projects.modal.title_new':       'New Project',
   'projects.modal.name':            'Name',
   'projects.modal.name_ph':         'My Project',
-  'projects.modal.path':            'Path',
-  'projects.modal.path_ph':         '/path/to/project',
   'projects.modal.desc':            'Description',
   'projects.modal.desc_ph':         'What this project is about',
   'projects.modal.cancel':          'Cancel',
@@ -199,36 +200,22 @@ export default {
   'projects.modal.save':            'Save',
   'projects.modal.create':          'Create',
 
-  // ── Project board ───────────────────────────────────────────────────────────
+  // ── Project sharing ─────────────────────────────────────────────────────────
+  'projects.share.title':           'Sharing',
+  'projects.share.owner':           'owner',
+  'projects.share.choose_user':     'Choose a person…',
+  'projects.share.add':             'Add',
+  'projects.share.all_added':       'Everyone already has access.',
+  'projects.share.remove':          'Remove',
+  'projects.share.access.read':     'Read',
+  '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.',
+
+  // ── Project detail ──────────────────────────────────────────────────────────
   'project_board.back':               'Projects',
   'project_board.open_chat':          'Open Chat',
-  'project_board.new_ticket':         'New Ticket',
-  'project_board.tab.tickets':        'Tickets',
-  'project_board.section.running':    'Running',
-  'project_board.section.running_empty': 'No tickets running',
-  'project_board.section.todo':       'Todo',
-  'project_board.section.todo_empty': 'No tickets to do',
-  'project_board.section.completed':  'Completed',
-  'project_board.section.completed_empty': 'No completed tickets',
-  'project_board.ticket.start':       'Start',
-  'project_board.ticket.running':     'Running…',
-  'project_board.ticket.reset':       'Reset',
-  'project_board.ticket.result':      'Result',
-  'project_board.ticket.error':       'Error',
-  'project_board.ticket.no_output':   '(no output)',
-  'project_board.ticket.no_error':    '(no error message)',
-  'project_board.modal.title':        'New Ticket',
-  'project_board.modal.title_label':  'Title',
-  'project_board.modal.title_ph':     'What needs to be done',
-  'project_board.modal.desc_label':   'Description / Prompt',
-  'project_board.modal.desc_ph':      'Detailed instructions for the agent…',
-  'project_board.modal.agent':        'Agent',
-  'project_board.modal.security_group':'Security Group',
-  'project_board.modal.inherit':      '— inherit from project —',
-  'project_board.modal.cancel':       'Cancel',
-  'project_board.modal.saving':       'Saving…',
-  'project_board.modal.create':       'Create',
-  'project_board.confirm.delete':     'Delete ticket "{title}"?',
 
   // ── Session detail ──────────────────────────────────────────────────────────
   'session.back':             'Back',