Removing community apps in favor of npm-distributed apps (#20029)

## Context
With the registry pattern around `Twenty Applications` and the upcoming
marketplace, app
distribution can be decoupled from the core repo. Pulling apps from npm
instead of
shipping them in-tree means:

- Contributors don't clone / index / build code for apps they'll never
touch
- Each app can version, release, and iterate independently of the core
cadence
- We stop carrying apps that are effectively unmaintained in the
monorepo

## How
This PR removes the 11 community apps from
`packages/twenty-apps/community/`

## Note
- **Marketplace apps** must be published on npm and pulled from there —
no app code living in this repo just to be distributed
- **Showcase / example apps** stay as living examples of what the SDK
can do under `example/`
- **Officially-maintained marketplace apps** (like the new
`github-connector`?) stay in the repo under `internal/`. Some may be
pre-installed on new workspaces alongside the Standard app

Author: Weiko