docs: split Linux packages guide into quick start, operations, and offline pages

The Linux Packages Quick Start had grown to 2,335 words and 7 callouts,
mixing a first-install path with day-2 operations, air-gapped installs and
platform caveats. A reader installing on a supported host had to skip most
of the page to find the five commands they needed.

Split it into three pages:

- Linux Packages Quick Start (842 words) - install, set up, connect, verify.
  One callout, kept because it corrects a genuinely misleading default: the
  wizard binds all interfaces while the connect string says 127.0.0.1.
- Linux Packages: Operations - securing the listener, services and paths,
  running SQL, upgrading, removal, non-systemd hosts, known issues in 0.116.
- Linux Packages: Offline Install - staging a dependency closure and
  installing on an air-gapped target.

All three are registered in getAllArticlePaths and the Getting Started
sidebar, so neither new page is reachable only through in-content links.

No install instruction changed; this is a reorganisation of existing text.

Author: GuanzhouSong