docs: Add multiuser documentation and reposition Workflows (#9099)

* docs: added multi-user mode and moved workflows under features

* docs: finish moving workflows under features/

* Update docs/src/content/docs/features/Canvas/text-tool.mdx

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* Update docs/src/content/docs/features/hotkeys.mdx

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* docs(multiuser): fix links, remove redundant sections

* Update docs/src/content/docs/features/Multi-User Mode/api-guide.mdx

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* docs(multiuser): address issues raised in 6 May review

* Update docs/src/content/docs/features/Multi-User Mode/api-guide.mdx

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* Update docs/src/content/docs/features/Multi-User Mode/api-guide.mdx

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* docs(multiuser): more doc fixes

* docs(multiuser): remove outdated jwt config entries and reword strong password requirement

* Apply suggestions from code review

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* docs(multiuser): fixed errors identified in review

* Update docs/src/content/docs/features/Multi-User Mode/admin-guide.mdx

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>

* docs(multiuser): correct API and UI inaccuracies flagged in review

Reviewer comments pointed out several places where the multi-user docs
described behavior the code does not implement. Each item was verified
against the source before updating the docs.

- api-guide: create-board examples use board_name as a query parameter
  (not a JSON body) to match the FastAPI Query() declaration in
  boards.py.
- api-guide: the "all endpoints require authentication" list now
  includes the three intentionally unauthenticated image/thumbnail
  endpoints, with the UUID-unguessability rationale used in the code
  comments.
- api-guide: /auth/status sample response now shows both the
  setup_required=true and setup_required=false states, with a note
  that admin_email is only populated during initial setup.
- admin-guide: delete-user warning no longer claims that all of a
  user's content is removed; it now lists what actually cascades
  (sessions, shared_boards, invitations sent, client_state) and what
  is left orphaned (boards, images, workflows, queue items, style
  presets, plus on-disk image files).
- admin-guide: removed the hallucinated "Admin -> Queue Overview"
  navigation and per-user filter; the actual admin queue experience is
  the regular queue panel showing all users' items, with no built-in
  user filter.
- admin-guide: fixed broken relative link to user-guide
  (../user-guide -> ./user-guide; same folder).
- user-guide: queue badge description corrected -- it is a single
  count of the user's own pending + in_progress items, not an X/Y
  ratio.
- user-guide: admin badge location corrected -- the user menu lives
  near the bottom of the left-hand nav bar, and the "Admin" badge
  appears inside the dropdown, not in the top-right corner.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Josh Corbett <joshwcorbett@icloud.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>