12: Delete all tutorials

[mnocon]

Ticket 12 of the Cohesivo SaaS conversion. Base: saas-batch-3.

Deletes all three tutorials. Every one of them opens by asking for a local
installation and ends by writing a template or a PHP class, none of which a
Cohesivo tenant can do. All three go rather than being partially stripped: a
tutorial that no longer reaches a working result is worse than no tutorial.

A replacement SaaS getting-started tutorial is separate work, explicitly out of
scope here.

Changes

• 71 files deleted: 25 pages (docs/tutorials/ in full — beginner,
  page-and-form, generic field type, and the landing page) plus 46 images and
  assets used only by them, each checked for other referrers first.
• The Tutorials nav section is removed from mkdocs.yml.
• 10 surviving pages had inbound links removed.

The front page

The front page's primary entry tile pointed at the beginner tutorial, so it is
gone. The remaining "APIs" and "First steps" tiles still form a coherent row —
the ticket requires the page stay coherent, not that it be rebuilt, and the full
rebuild is ticket 19's job. No redesign was attempted here.

Judgement calls

• docs/users/user_registration.md was kept, not deleted. Beyond the dead
  tutorial link it carries real content — user types, groups, form
  configuration, password templates — so only the link was replaced, with a
  pointer to the anonymous user/register policy.
• ibexa_connect_scenario_block.md: only the tutorial sentence was dropped. The
  notes suggested removing the whole admonition, but it also carried an
  unrelated profiler caution worth keeping.
• add_image_asset_from_dam.md was repointed at page_blocks.md;
  content_management_guide.md lost its custom-field-type clause outright.

Three links fixed beyond the ticket's list

The notes flagged three dangling links as "referrer deleted by ticket 09/11".
Those tickets have not merged yet, so on this branch the links were live and
would have failed --strict. All three are fixed here
(create_custom_generic_field_type.md, extend_image_editor.md,
project_organization.md), which keeps this branch green standalone and is a
no-op once 09 and 11 delete those files.

Verification

• mkdocs build --strict → exit 0.
• pytest -q → 95 passed (this branch predates ticket 01's five new tests).
• Grep of the built site/ for tutorial paths: no leftover internal links. The
  only hits are an external doctrine-project.org/.../tutorials/... URL.

invariants-baseline.yaml untouched, no new files under docs/, and the
mkdocs.yml edit is confined to the Tutorials block so it merges cleanly
alongside the sibling deletion tickets.

🤖 Generated with Claude Code

[github-actions]

Preview of modified files

Preview of modified Markdown:

• docs/administration/project_organization/project_organization.md
• docs/content_management/content_management_guide.md
• docs/content_management/field_types/create_custom_generic_field_type.md
• docs/content_management/images/add_image_asset_from_dam.md
• docs/content_management/images/extend_image_editor.md
• docs/content_management/pages/ibexa_connect_scenario_block.md
• docs/getting_started/first_steps.md
• docs/index.md
• docs/tutorials/beginner_tutorial/1_get_ready.md
• docs/tutorials/beginner_tutorial/2_create_the_content_model.md
• docs/tutorials/beginner_tutorial/3_customize_the_front_page.md
• docs/tutorials/beginner_tutorial/4_display_single_content_item.md
• docs/tutorials/beginner_tutorial/5_display_a_list_of_content_items.md
• docs/tutorials/beginner_tutorial/6_improve_configuration.md
• docs/tutorials/beginner_tutorial/7_embed_content.md
• docs/tutorials/beginner_tutorial/8_enable_account_registration.md
• docs/tutorials/beginner_tutorial/beginner_tutorial.md
• docs/tutorials/generic_field_type/1_implement_the_point2d_value_class.md
• docs/tutorials/generic_field_type/2_define_point2d_field_type.md
• docs/tutorials/generic_field_type/3_create_form_for_point2d.md
• docs/tutorials/generic_field_type/4_introduce_a_template.md
• docs/tutorials/generic_field_type/5_add_a_field.md
• docs/tutorials/generic_field_type/6_settings.md
• docs/tutorials/generic_field_type/7_add_a_validation.md
• docs/tutorials/generic_field_type/8_data_migration.md
• docs/tutorials/generic_field_type/creating_a_point2d_field_type.md
• docs/tutorials/page_and_form_tutorial/1_get_a_starter_website.md
• docs/tutorials/page_and_form_tutorial/2_prepare_the_landing_page.md
• docs/tutorials/page_and_form_tutorial/3_use_existing_blocks.md
• docs/tutorials/page_and_form_tutorial/4_create_a_custom_block.md
• docs/tutorials/page_and_form_tutorial/5_create_newsletter_form.md
• docs/tutorials/page_and_form_tutorial/page_and_form_tutorial.md
• docs/tutorials/tutorials.md
• docs/users/user_registration.md