Prepare v0.9.9.2 release - #43

Summary

• prepare the v0.9.9.2 release
• align release ZIP naming to swift-csv-<version>.zip so it matches the updater expectation
• bump plugin/package versions to 0.9.9.2
• fix Docsify language navigation by splitting English and Japanese sidebars and correcting the language switcher links
• update README and docs download references for 0.9.9.2

Background

• v0.9.9 used the GitHub zipball_url, which caused random extracted directory names during updates
• v0.9.9.1 includes the updater fix, so v0.9.9.1 -> v0.9.9.2 is the path we want to verify next
• this PR also makes the release asset name deterministic and consistent with the updater lookup

Testing

• confirmed the updater now resolves release asset URLs instead of relying on plugin-local banner/icon paths
• updated the release workflow to publish swift-csv-<version>.zip
• updated the local test release script to generate the same v-less ZIP naming
• verified Docsify config now uses separate sidebars for English and Japanese routes

Follow-up

• after merging, create and push tag v0.9.9.2
• verify the staging site can update from 0.9.9.1 to 0.9.9.2 and restores the normal swift-csv/ plugin directory flow