docs(dev): correct 15.8 plugin architecture guide against implementation

[marevol]

Summary

Reviewed the developer plugin-architecture guide (15.8/dev/plugin-architecture.rst) against the current Fess source code and corrected several inaccuracies, then propagated the corrected content to all languages (ja, en, de, fr, es, ko, zh-cn). The Japanese version was verified first and used as the source for the translations.

Corrections

• Plugin types — Listed all categories recognized by PluginHelper.ArtifactType (data store, web app, script engine, ingest, theme, thumbnail, LLM, crawler) with their artifact-name prefixes, and noted the list is not exhaustive.
• Plugin structure — Replaced the fabricated layout with the real fess-ds-example structure and added the fess_ds++.xml registration file. Removed the non-existent ExampleDataStoreHandler.java.
• pom.xml — Inherit from fess-parent and declare fess / opensearch with provided scope (matching the real reference plugin).
• Registration — Documented the ++ DI merge convention (fess_ds++.xml, fess_se++.xml, fess_ingest++.xml, fess_llm++.xml, app++.xml). Fixed register() to call ComponentUtil.getDataStoreFactory().add(getName(), this), and clarified it runs via the <postConstruct> element rather than the Java @PostConstruct annotation.
• storeData() — Corrected the signature to use DataStoreParams (not Map<String, String>) and getAsString() for parameter access; getName() is protected.
• Installation — Install from the admin console (select from the plugin repository list or upload a JAR), or copy the JAR to app/WEB-INF/plugin/. Removed the non-existent CLI command.
• Misc — Referenced the IDE boot class org.codelibs.fess.FessBoot, refreshed the published-plugin list, and added links to theme-development and the plugin installation guide.

Verification

• All examples checked against fess-ds-example, AbstractDataStore, PluginHelper, ResourceUtil, and AdminPluginAction.
• Structural parity across all 7 languages verified (code blocks, tables, :doc: targets, |Fess| substitutions), no residual source-language text, proper diacritics for de/fr/es, and valid RST section underlines.