docs(admin/occ): complete user & group command documentation

Add missing commands:
- user:auth-tokens:add/delete/list — app password management
- user:clear-avatar-cache — clear cached avatars
- user:keys:verify — verify E2E encryption key pair
- user:list — expanded with options (--disabled, --info, pagination)
- user:info — rewritten with accurate output example
- user:sync-account-data — sync backend data to accounts table
- user:welcome — send welcome email with optional password reset link
- group:info — show group details and backend
- group:list — add searchstring argument and output options
- twofactorauth:enforce — enforce 2FA globally or per group
- twofactorauth:state — show 2FA state for a user
- twofactorauth:cleanup — clean up removed provider associations
- tag:files:add/delete/delete-all — assign system tags to files

Writing quality improvements:
- Fix user:profile examples (missing sudo prefix)
- Rewrite user:list and user:info intros
- Fix user:report backtick formatting
- Mark user:add-app-password as deprecated
- Restructure user:disable/enable into a named section; note that
  sessions are invalidated within 5 minutes, not immediately, with
  a pointer to user:auth-tokens:delete for immediate invalidation
- Restore accurate newUser.sendEmail default behaviour note
- Update group command listing to include group:info
- Expand 2FA section with full command listing and new commands
- Rewrite System Tags section with concrete examples and real output;
  add per-command headings; escape tag:* headings to prevent docutils
  treating 'tag:' as a URI scheme (RFC 4151); note tag:edit --color=""
  workaround; link access levels to automated_tagging docs; clarify
  that tag:files:add access identifies the tag and auto-creates it
- Standardize all examples to use layla as the example user
- Use milliways as the example group name

AI-Assisted-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Anna Larch <anna@nextcloud.com>

Author: miaulalala