fix(types): resolve TS2411 errors under strict TypeScript settings

[nbouvrette]

Summary

• Change index signatures from [k: string]: string to [k: string]: string | undefined in three locations (engines, volta, esnext object variant) in src/types.d.ts
• Under strict TypeScript, optional named properties have type string | undefined, which conflicts with an index signature typed as [k: string]: string, producing TS2411 errors
• Widening the index signature to string | undefined resolves all four errors

Errors fixed

dist/index.d.ts(277,5): error TS2411: Property 'node' of type 'string | undefined' is not assignable to 'string' index type 'string'.
dist/index.d.ts(287,5): error TS2411: Property 'extends' of type 'string | undefined' is not assignable to 'string' index type 'string'.
dist/index.d.ts(356,9): error TS2411: Property 'main' of type 'string | undefined' is not assignable to 'string' index type 'string'.
dist/index.d.ts(357,9): error TS2411: Property 'browser' of type 'string | undefined' is not assignable to 'string' index type 'string'.

Changes

Type	Location	Optional property
engines	line ~278	node?: string
volta	line ~292	extends?: string
esnext object variant	line ~358	main?: string, browser?: string

Note on source

src/types.d.ts is auto-generated from the upstream JSON Schema at schemastore.org via pnpm build:upstream. Since the upstream schema cannot be changed here, the fix is applied directly to the generated source file — consistent with the existing src/patch/ pattern used in this repo.

🤖 Generated with Claude Code