docs(15.9): rename the GCS plugin and replace the Library plugin type

[marevol]

Follows codelibs/fess#3426 and codelibs/fess-storage-gcs#1. Merge after fess#3426, so the docs never name a plugin that does not exist.

Fess names plugin types after the extension point they plug into — fess-ds is a DataStore, fess-script a ScriptEngine, fess-llm an LLM client. fess-lib-* named the content instead ("a third-party client and its dependencies"), so it is replaced by fess-storage-* and fess-sso-*, and fess-lib-gcs becomes fess-storage-gcs. Nothing was published under the old name, so this is a rename rather than a migration note.

The plugin name

Updated in the six 15.9 pages that mention it, in all seven languages: install/upgrade.rst, config/crawler-advanced.rst, admin/storage-guide.rst, admin/fileconfig-guide.rst, admin/general-guide.rst, dev/plugin-architecture.rst. 34 files, 73 occurrences.

The plugin type table

dev/plugin-architecture.rst loses its Library row and gains two:

type	prefix	description
Storage	fess-storage-*	Adds an object storage backend for crawling and for the storage feature
SSO	fess-sso-*	Adds a single sign-on authenticator selected by sso.type

No fess-sso-* plugin exists yet — saml, entraid, spnego and oic still ship in core. The row is here because the page documents the prefixes Fess recognises and its audience is developers reading that list; the alternative was editing the same table in seven languages again a release later.

Wording came from each tree rather than fresh translation. The type name matches the admin/storage-guide.rst title in each language (Speicher / Almacenamiento / Stockage / 스토리지 / 存储), "object storage" matches each tree's existing term, the authenticator wording follows the phrasing of the adjacent Thumbnail row, and Single Sign-On stays in English in de/es/fr as config/sso-*.rst already has it.

Verification

All 41 files parsed with docutils before and after, doctitle_xform=False the way Sphinx parses, with the conf.ini [replace] substitutions prepended so |Fess| resolves:

• system messages: zero diff per file (compared as counters with line prefixes stripped, since edits shift line numbers)
• no markup left unparsed in the rendered text
• the same number of top-level sections
• table rows +1 on exactly the seven plugin-architecture.rst, unchanged elsewhere; each new row has three cells, and fess-storage-*, fess-sso-* and sso.type all parsed as literal nodes — the check that catches an inline start-string sitting against a CJK character, which docutils drops silently

The markup checks were confirmed non-vacuous against known-broken inputs (ASCII- and CJK-adjacent **bold** and ``code``, plus a deliberately broken table row) and against correct controls, so they are not simply always-red.

Pre-existing issues found, not fixed

Identical in HEAD and here, in all seven languages, and unrelated to this change — both are docutils not parsing nested inline markup, so a literal ships raw to the reader:

• config/crawler-advanced.rst (en:1333) — - **Waiting for ``renderedState``**:
• install/upgrade.rst (en:345) — a |Fess| substitution inside **bold**

Also confirmed: ko/15.9/admin/fileconfig-guide.rst is missing the GCS note the other six carry, and ko/15.9/admin/storage-guide.rst is an earlier translation whose overview still describes MinIO only.