adds syntax highlighting from shiki which server side renders, and adds a copy text button #5

src/lib/highlight.ts uses shiki to parse code and output as html, uses catppuccin-latte and catppuccin-mocha as its themes.

src/public/styles.css added css for the shiki highlighted code blocks and button, query for the reactive theme switching for shiki

src/views/index.pug added nix and bash as language options

package.json & package-lock.json added shiki dependency (^3.4.2)

src/routes.ts integrated the highlighting system - processes code through shiki before rendering.

src/views/paste.pug replaced regex based line splitting with the shiki processed html