feat(config): ship JSON Schema for ripple.config.json (editor autocomplete)

[alimaandev]

Add JSON Schema support for the JSON config variant (ripple.config.json). The CLI already ships a JSON Schema for editor validation (see src/config/schema.ts); wire it into the package so editors pick it up automatically.

Acceptance criteria

• A ripple.config.schema.json is shipped in the npm package and referenced from the published JSON config docs.
• When a user opens their ripple.config.json, editors with the VS Code JSON language server show autocomplete for include, ignore, aliases, diff.base, diff.gate and the rest of the documented surface.
• A short README section ("Editor support") explains how to wire it up in VS Code via json.schemas.

Where to look

• src/config/schema.ts (generated schema), docs/ or README config section, package.json files field.

Out of scope

• JSONC/TS config variants (they are code, not data).