Fixes #20770

Fixes #20550

* Fix missing pagination headers on followed tags

* Fix typo

Several controlers set quite intricate Cache-Control headers in order to
hopefully not be cached by any intermediate proxies or local caches. Unfortunately,
these headers are processed by ActionDispatch::HTTP::Cache in a way that squashes
and discards any values set alongside no-store other than private:
https://github.com/rails/rails/blob/8015c2c2cf5c8718449677570f372ceb01318a32/actionpack/lib/action_dispatch/http/cache.rb#L207-L209

We want to preserve no-store on these responses, but we might as well remove
parts that are going to be dropped anyway. As many of the endpoints in these
controllers are private to a particular user, we should also add "private",
which will be preserved alongside no-store.

* Move V2 Filter methods under /api/v2 prefix

* move over the tests too

Fix #19156

Fix #19157

* Remove dead code

* Remove unneeded/broken parameters and refactor descendant computation

```ruby
10.times { p /#{FOO}/.object_id }
10.times { p FOO_RE.object_id }
```

* Make account endorsements idempotent (fix #19045)

* Accept suggestion to use exists? instead of find_by + nil check

Co-authored-by: Yamagishi Kazutoshi <ykzts@desire.sh>

* fix logic (unless, not if)

* switch to using `find_or_create_by!`

Co-authored-by: Yamagishi Kazutoshi <ykzts@desire.sh>

Fixes #19913

New environment variable `DISALLOW_UNAUTHENTICATED_API_ACCESS`

Fixes #19593

Fixes #19507

Fix regression from #19296

Fix #19153

Fix #19542

Fix #19213

* Add ability to view previous edits of a status in admin UI

* Change moderator access to posts to be controlled by a separate policy

- Only exact search matches for queries with < 5 characters
- Do not support queries with `offset` (pagination)
- Return HTTP 401 on truthy `resolve` instead of overriding to false

Regression from #19409

* Change featured tag updates to add/remove activity

* Fix to check for the existence of feature tag

* Rename service and worker

* Merge AddHashtagSerializer with AddSerializer

* Undo removal of sidekiq_options

And update all descriptions

* Change public accounts pages to mount the web UI

* Fix handling of remote usernames in routes

- When logged in, serve web app
- When logged out, redirect to permalink
- Fix `app-body` class not being set sometimes due to name conflict

* Fix missing `multiColumn` prop

* Fix failing test

* Use `discoverable` attribute to control indexing directives

* Fix `<ColumnLoading />` not using `multiColumn`

* Add `noindex` to accounts in REST API

* Change noindex directive to not be rendered by default before a route is mounted

* Add loading indicator for detailed status in web UI

* Fix missing indicator appearing while account is loading in web UI

* Add LIMIT of featured tag to instance API response

* Add featured_tags_collection_url to Account

* Add synchronization of remote featured tags

* Deliver update activity when updating featured tag

* Remove featured_tags_collection_url

* Revert "Add featured_tags_collection_url to Account"

This reverts commit cff349fc27b104ded2df6bb5665132dc24dab09c.

* Add hashtag sync from featured collections

* Fix tag name normalize

* Add target option to fetch featured collection

* Refactor fetch_featured_tags_collection_service

* Add LIMIT of featured tag to v1/instance API response

Previously all controllers would use the single "No accounts changed as
none were selected" message. This commit changes them to read "tags",
"posts", "emojis", etc. where necessary.

Source string no longer localized, Markdown instead of raw HTML