Require Cursor 3.13.0 for the Google Workspace plugins

[maloneya]

The six Google Workspace plugins added in #179 depend on client behavior that only exists in Cursor 3.13.0 and newer. This sets "minClientVersions": { "cursor": "3.13.0" } on each of their manifests so older clients don't install them.

schemas/plugin.schema.json has additionalProperties: false, so the key had to be allowed in the schema first, otherwise scripts/validate-plugins.mjs rejects the manifests.

Changes

• schemas/plugin.schema.json: new optional minClientVersions object keyed by client identifier. cursor is documented explicitly; other client identifiers are permitted and constrained to the same version format. Values must be strict semver X.Y.Z with an optional prerelease suffix, and the object must have at least one entry.
• schemas/marketplace.schema.json: same field added to the pluginEntry definition, which also has additionalProperties: false. No entries in .cursor-plugin/marketplace.json set it today; this only makes it expressible.
• gmail/, google-calendar/, google-docs/, google-drive/, google-sheets/, google-slides/: each .cursor-plugin/plugin.json now declares the 3.13.0 minimum.

Verification

node scripts/validate-plugins.mjs passes. I also checked the schema directly against a handful of inputs: 3.13.0 and 3.13.0-beta.1 are accepted, and 3.13, v3.13.0, an empty object, and a bare string are all rejected.