fix(manifest): satisfy the Tabularium driver-kind contract

[NewtTheWolf]

The .tabularium migration renamed the file but kept the legacy manifest.json field set, so the registry rejects this manifest today. Verified against POST https://registry.tabularis.dev/api/manifest/validate: this branch returns ok: true, the current default branch does not.

Change	Why
name → "libsql"	Core schema requires ^[a-z][a-z0-9-]*$. name is both the registry slug and the plugin identity.
dropped id	Removed from the core schema. The host falls back to name, which is set to the old id value, so the driver key and existing connections are unchanged.
dropped $schema	Pointed at tabularis.dev/schemas/plugin-manifest.json, which no longer exists.
added kind, engine, paradigms	engine and paradigms are required for the driver kind; they drive catalogue grouping and the filter chips.
dropped default_port	Was null; the schema wants an integer, and the field is meant to be omitted for file-, folder- and API-based drivers.

No version bump: this repo has no release that the fix would need to supersede. Tag one when ready and the corrected manifest ships with it.