fix: migrate Deno standard library imports to JSR

[luojiyin1987]

Summary

• Move standard library imports to JSR aliases.
• Declare all dependency aliases in deno.json.
• Replace any values in render_svg.ts.
• Use a Deno 1.44.4 and Deno 2.x CI matrix.
• Make lint errors fail CI.

Root cause

The project used mixed deno.land/std versions and JSR imports.
Deno 2 lint rejects inline dependency URLs.
The former CI only ran Deno 1.44.4. It ignored lint errors.

Local Deno 2 validation

Validated with Deno 2.9.0.

• deno fmt --check
• deno lint
• deno test --allow-env

Closes #455