Refactor internal addon references to app/apps (#6717)

* Rename addon→app in docstrings and comments

Updates all docstrings and inline comments across supervisor/ and
tests/ to use the new app/apps terminology. No runtime behaviour
is changed by this commit.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Rename addon→app in code (variables, args, class names, functions)

Renames all internal Python identifiers from addon/addons to app/apps:
- Variable and argument names
- Function and method names
- Class names (Addon→App, AddonManager→AppManager, DockerAddon→DockerApp,
  all exception, check, and fixup classes, etc.)
- String literals used as Python identifiers (pytest fixtures,
  parametrize param names, patch.object attribute strings,
  URL route match_info keys)

External API contracts are preserved: JSON keys, error codes,
discovery protocol fields, TypedDict/attr.s field names.
Import module paths (supervisor/addons/) are also unchanged.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix partial backup/restore API to remap addons key to apps

The external API accepts `addons` as the request body key (since
ATTR_APPS = "addons"), but do_backup_partial and do_restore_partial
now take an `apps` parameter after the rename. The **body expansion
in both endpoints would pass `addons=...` causing a TypeError.

Remap the key before expansion in both backup_partial and
restore_partial:

    if ATTR_APPS in body:
        body["apps"] = body.pop(ATTR_APPS)

Also adds test_restore_partial_with_addons_key to verify the restore
path correctly receives apps= when addons is passed in the request
body. This path had no existing test coverage.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix merge error

* Adjust AppLoggerAdapter to use app_name

Co-authored-by: Stefan Agner <stefan@agner.ch>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Stefan Agner <stefan@agner.ch>

Author: 3 people

supervisor/addons/__init__.py

@@ -1 +1 @@
-"""Init file for Supervisor add-ons."""
+"""Init file for Supervisor apps."""