Rename package to pdfkernel

[michaelgbcole]

What changed

• Renamed the published package metadata from @folsom/tspdf to pdfkernel.
• Updated repository, homepage, issue, badge, install, and import URLs for the renamed GitHub repository and npm package.
• Replaced the old project name throughout source documentation, benchmarks, and tests.
• Updated the Bun workspace name to match the package.

Why

The repository has been renamed to pdfkernel, and the package name should communicate that this is a PDF core rather than a renderer while staying consistent across GitHub, npm, docs, and code examples.

Developer impact

After the new package is published, consumers should install and import pdfkernel:

npm install pdfkernel

import { PdfDocument } from "pdfkernel";

The existing @folsom/tspdf@0.1.0 npm release will need to be deprecated separately with a pointer to pdfkernel; npm packages cannot be renamed in place.

Validation

• bun run check
• bun run build (publint and are-the-types-wrong pass)
• bun run test
• bun run gate:spec (64/64)
• npm pack --dry-run (pdfkernel@0.1.0, 11 files)
• Confirmed no tracked references to the old name remain

Local Bun is 1.3.10 while the repo lockfile targets Bun 1.4, so build/package validation was run with the lockfile temporarily set aside and restored unchanged.