feat: validate and normalize input data

[Vtec234]

• Enforce stricter constraints on project/user/template names/IDs - ASCII and no special characters besides hyphens and underscores; see the diff in src/lib/util.ts.
• Consistently validate input data across server functions and authentication code.
• Compare user/project names up to casing in SQL. Fixes Enforce ASCII-only, case-insensitive user and project names #23.

Also a few misc changes:

• Factor out Error component.
• Replace node:fs with node:fs/promises in user profile actions.
• Return 404 instead of a rendered error in project pages with incorrect URL.
• Remove old test scripts.