Weave the shutdown hook into the lifecycle docs

Rolled down from the stack's docs-only tip PR: lifecycle step 5 now
describes shutdown-hook ordering, and the shutdown() hook docs
cross-reference the lifecycle and background-task sections.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012U7coQfVu8nK2R4q2mCULA

docs/internals.rst

@@ -1416,7 +1416,7 @@ Datasette guarantees a fixed sequence of events between the moment a ``Datasette
 2. **Startup** — ``await datasette.invoke_startup()`` runs once: it populates the internal database's catalog of table schemas (:ref:`internals_internal`), loads canned queries and column type configuration, then calls every registered :ref:`plugin_hook_startup` hook, in plugin registration order. When Datasette is being served, table-count precomputation for immutable databases runs immediately before this, as part of the same startup sequence.
 3. **Background-task launch** — once *every* ``startup`` hook has finished (not before), every task registered with :ref:`datasette_add_background_task` — by any plugin — is launched. A task registered by one plugin's ``startup`` hook can safely depend on state set up by another plugin's ``startup`` hook, because launch only happens after the whole round of hooks completes.
 4. **Serving** — the instance handles requests (or, for headless or CLI use, does whatever the embedding program does with it).
-5. **Shutdown** — triggered by the ASGI ``lifespan.shutdown`` event (Ctrl-C, ``SIGTERM``) or the end of a ``datasette serve`` process: every still-running background task is cancelled and given a five-second grace period to actually stop; finally every database connection is released via :ref:`datasette_close`.
+5. **Shutdown** — triggered by the ASGI ``lifespan.shutdown`` event (Ctrl-C, ``SIGTERM``) or the end of a ``datasette serve`` process: every :ref:`plugin_hook_shutdown` hook runs first, while background tasks are still alive, so a plugin can tell its own task to wind down gracefully; every still-running background task is then cancelled and given a five-second grace period to actually stop; finally every database connection is released via :ref:`datasette_close`.
 
 .. admonition:: Startup hooks run on the event loop that serves requests
 

docs/plugin_hooks.rst

@@ -1221,7 +1221,7 @@ This hook fires once, when the Datasette application server is shutting down gra
 
 Like ``startup()``, this can be a regular function or it can return an async function to be awaited.
 
-It runs before Datasette cancels any background tasks it is supervising and before it closes its database connections, so you can use it to tell your plugin's own background work to stop gracefully while a database connection is still available to write out any final state:
+It runs before Datasette cancels any background tasks it is supervising (see :ref:`datasette_add_background_task`) and before it closes its database connections, so you can use it to tell your plugin's own background work to stop gracefully while a database connection is still available to write out any final state. See :ref:`datasette_lifecycle` for exactly where this fits into the full startup-to-shutdown sequence:
 
 .. code-block:: python