feat: migrate to the .tabularium manifest for the Tabularium registry

[NewtTheWolf]

Migrates this plugin from the legacy manifest.json to the canonical .tabularium bundle manifest that the Tabularis host now reads and the hosted Tabularium registry requires (the registry resolves the manifest from release assets, so .tabularium must be published as a standalone asset).

Generated with @tabularis/create-plugin migrate.

This repo has custom CI steps, so the release workflow was kept instead of regenerating it from the template (migrate without --ci); it was made registry-ready by hand:

• .tabularium written from manifest.json; manifest.json removed
• README.md / sync.sh / workflow references renamed
• release job: added a checkout step and .tabularium as a standalone release asset
• id kept (differs from name, so it is the plugin identity)

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (4 files)

• .github/workflows/release.yml
• .tabularium
• README.md
• sync.sh

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_{Reviewed by step-3.7-flash · Input: 69.9K · Output: 5.1K · Cached: 146K}