Add TypeScript declaration file

[jstayton]

No description provided.

[Copilot]

Pull request overview

Adds TypeScript typings to the @truepic/webhook-verifier package so TS consumers get type checking and editor IntelliSense when using the existing CommonJS API.

Changes:

• Added src/main.d.ts declaration file describing verifyTruepicWebhook and its error type.
• Wired the declaration file into publishing/consumption by adding "types" to package.json.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
src/main.d.ts	Introduces TS declarations for the exported function and related error/options types.
package.json	Points TypeScript to the shipped .d.ts via the "types" field.

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